It's bound to happen sooner or later.  If you stay in this hobby long enough, it will eventually happen to you.
    Scenario:  You have a custom you want to make.  As you search through yet another clearance bin, you find the perfect base!  Well...almost perfect.  Maybe the legs are too short.  Or the arms aren't in the position you want.  Or maybe the torso is twisted into some bizarre stance.  Or, if you're looking at a wrestling figure, maybe all of the above.  ;)
    Just because something in the posture of a base figure isn't quite what you're looking for, does that mean you should abandon that base entirely?  Not really.  As you get more comfortable with advanced customizing techniques, you should train yourself to "think outside the box" when considering bases.  Just because something is fundamentally "wrong" with the sculpt of a base as far as your project is concerned, with a few relatively simple modifications you can make it "right."  And in the process, you can make a figure shorter, or taller, or pretty much whatever you desire.
    To illustrate this process, I will be working with a Jakks Pacific Grudge Match Sable action figure, in the 6" scale.  What follows is merely an introduction to the various structural modifications that can be made to an action figure.  These concepts can be used to make many other changes that I won't get into; your imagination is the limit!

** Many thanks to Ron Kenyon for our discussions on straightening a hollow torso.

    So from the list I have made above, you can get an idea of the changes I want to make.  I want to straighten her midsection so that her spine basically follows a straight line.  In the process, her hips will be straightened back in line with the rest of her torso.  As a consequence, her legs will both have to be repositioned into a more natural stance.
   Now, it's important to THINK before you start making drastic cuts into a figure.  After considering the Sable figure from all angles, you can see where I have decided to implement the changes.  You can see as I have done here, that it is a good idea to use a sharp pencil to draw a line where you will be making cuts.  The more planning you do at this stage, the easier the final conversion and adjustments will be.  The red arrows in the picture point to the lines I have drawn.  I will be cutting her torso in two places, and cutting each leg at the junction of the thigh to the hip.  When cutting near a joint, make the cut at least 1/4" away from the joint peg, to avoid weakening the joint.


    You can see here that I have made all necessary cuts.  I tend to use a Dremel rotary tool, with a separating disk attachment.  This makes it a little easier to cut through the hard plastic of the torso.
    Looking at this picture, notice that the red arrows are pointing to torso pegs.  Most torso's have one or two pegs located within the torso.  These pegs help to stabilize and strengthen the torso, as well as to help keep its halves securely fastened together.  When cutting into the torso, you want to try to cut away from these pegs.
    Unfortunately, there's no real way to tell from the outside of a figure exactly where these pegs are going to be located.  Generally, one is right in the dead center of the torso, while one is usually right above the point where the hip peg connects to the torso.  Keep this in mind when planning your cuts.
    If you start cutting into the torso, and notice that in one point you aren't breaking through to the other side of the plastic, you're probably cutting into a torso peg.  Just slightly reposition the Dremel blade, and begin again.  Once the torso is separated, you can repair the peg if you feel it's necessary, using plumber's epoxy, Milliput or Magic Sculp.

    Once all the lines have been cut, use an X-Acto knife to trim away any melted plastic from the edges of the cut pieces, as well as to remove any loose plastic.  The cut surface doesn't need to be completely smooth, and actually you don't want it to be.  But just make sure you remove loose bits.
    Here, I have tentatively re-aligned the pieces of the Sable figure into her new stance.  You can see how much straighter her back is, as well as the stance of her legs.  All in all, this is a much more natural pose, in my opinion.
    Now comes the task of reassembling the figure in its new pose.  Unfortunately, it's no longer a matter of gluing the pieces together, as this results in weak connections that break easily.  Instead, we must use a method known as "pinning the connections."  This is basically a connection that is glued together, but reinforced with a metal pin.  If we were attaching a hand to a forearm, think of the glue as the skin and muscle, and the metal pin as the wrist bone inside the joint.  Many people use cut paper clips as pins, and this works fine.  I usually use thin gauge floral stem wire, as this is still strong yet slightly more flexible than paper clips, which helps in positioning the limb.
    To do this, you need to play around a little bit to get the pins positioned just right.  You also need to have a definite idea of the final pose you're working toward.

   To attach the legs, I'm going to use two pins in each leg.  First, using a small drill bit just slightly larger in diameter than the pins, drill two small holes about 3/16 - 1/4" apart into the hip part of the leg connection; drill each hole slightly more than 1/8" deep.  Keeping in mind the final position you want for the leg, drill two identical holes in the corresponding spots into the leg itself.  Now, cut two small pieces of wire about 1/2" long.  Insert each piece into a hole on the hip, and then insert the other ends into the holes in the leg.  Allowing the wire to flex and bend slightly, work the leg into the position you want.  Once you have the leg positioned, note how much excess needs to be cut out of each piece of wire.  Trim the wire pieces of the excess, and then re-assemble the leg with the two pins.
    Once you have the pins cut to the correct length so that the leg can be positioned as you like it, coat 1/2 of each pin with super glue, and then firmly place the coated half of each pin into a hole in the leg.  Hold the pins firmly in place while the glue sets.  Now, coat the remaining half of each pin with super glue.  Place the two pins into the holes on the opposite part of the connection, and insert the pins fully and move the leg into the position you are working for.  Hold the leg in this position for 30 seconds to a minute, until the glue sets completely.  The glued pins should now hold the two leg pieces firmly together.
    **Note - during this stage of forming the connection and establishing the final position of the legs, this is a good time to think about trying to make the feet level.  Try to glue these connections near a sturdy, level table, so that you can check the stance of the feet.  Try to position the legs so the feet will be level, allowing the final figure to stand steadily without support.  Of course, if this isn't possible, you can always cut and re-pin the ankles later.  ;)

  That is how you pin a connection.  Do the same thing for the other leg.  At this point, you should also pin the torso.  If the torso was solid, you could just use 2-3 pins in the manner described above.  If the torso is hollow, as it is in this case, you need to place pins at several points around the perimeter of the torso.  In this instance I want to place 4 pins, one at the front, one at the back, and one in each side.  To do this, carefully drill a hole in the middle of the thin piece of plastic of the torso.  If you accidentally drill through the side of the plastic, you can always fix it later with putty.  Follow the same procedure you used to pin the leg connection, keeping in mind the final position you want for the torso.  Once the holes are all drilled, glue a pin in each hole and use it to secure the connection as you did with the leg.  Do this until the torso is completely secured in the position you desire.
    Notice in this picture how the legs have each been secured with two pins, and how the new pose manages to keep both feet on a level plane.  This allows the figure to stand freely without support.  Also notice the pins placed around the perimeter of the torso, securing it in the new pose.

A word about proportions:  Something that must be taken into consideration when repositioning a figure like this, is the final proportions of the figure.  Without getting too technical, art theory says that human beings are "Eight heads" tall; that is, a person's height is the same as the height of their head, multiplied by 8.  Heroic figures are as much as a half head taller.  The ideal person is also "Two heads" wide.  The location of these boxes, each of which has the same outline size as the head, corresponds to different anatomical landmarks, such as just above the navel, the center of the pubis, just below the knees, etc.
    Now, when you cut off a leg, glue a pin in it and reposition it at a different angle, you are making that leg slightly longer.  The same goes for the arms, and the torso.  So by straightening Sable's torso and legs, I have made her significantly taller.  In instances like these, you might want to do a comparison of the figure in it's final posture, to make sure that you haven't thrown off the proportions too much.  This isn't absolutely necessary, but it does help you to make sure the figure will have a natural appearance.
    As you can see here, I am pretty lucky that Sable is still pretty much dead-on in her proportions (the last rectangle ends high on her feet because she's wearing high heels).  The knees look like they're a little higher than they should be, but that's because the legs are angled slightly away from her body.  The only real problem, is Sable's arms are now slightly short.  This could be fixed simply by making a straight cut through each bicep, and pinning the arms with a bit of length added to fit in with the rest of the body.
    All in all, her arms aren't too far off.  I'm going to leave it for now, and only fix it later if I think I have to.

   So now, we've got a figure that's positioned naturally and in the stance we want.  We also have a figure that has maintained good human proportions.  But there's all these gaps where we made the cuts, with metal pins visible.  This might work for a cyborg custom of some sort, but for our purposes we need to fill those gaps!  This is the fun part of the job.
    Basically, prepare your self-hardening sculpting compound of choice (Kneadatite, Milliput, Magic Sculp, etc.); I prefer Milliput because it self hardens, gets rock hard but can still be sanded glass smooth, and also bonds to the plastic, which further strengthens the connection.  Now use that to simultaneously fill the gaps, and blend the sculpt.  For solid sections like legs and arms, try to fill the gap as completely as possible with clay.  For the hollow torso, you want to limit how deep you place the clay.  As you recall from the early picture inside the torso, the pegs from the leg joints are just below one of the cuts on our torso.  If you were to push Milliput too far into the torso so that it came in contact with those pegs, and then bonded to them while curing, you would lock the pegs into position and prevent the legs from moving.  So keep an eye open for that while filling the gaps in the torso.
    So take the clay and start pushing it into the gaps you've created.  Once the gaps are filled, it's time to blend the sculpt.  This basically means sculpting into the clay to create a smooth transition between the sculpted lines in plastic on one side of a cut, with those on the other side of the cut.  For example, in the abdominal area, sculpt the clay so the lines of the stomach muscles are smooth and continuous.  You can also add more clay at this point to beef up areas that are asymmetrical; in this case, I am building up the left hip a little to match the curve of the right hip.  Make as much effort as possible to create a smooth transition between clay and plastic.
    Remember, the more time you spend working now, the more seamless the final connections will seem.

To Be Continued...