If you really want to be able to position your figures exactly the way you want them, there is a sure-fire method that is a bit more refined than melting with a lighter. A regular X-acto saw works fine, but for really delicate cuts or operating in tight places, get a jewler's saw. (X-acto makes these too). Jewler's saws can go places no other saw can, since the blade is only .02 inches wide and .010 inches thick, just the tool you need for lopping of heads, arms and legs, without messing up the rest of the figure. Saw off the offending arm, leg, hand or head. Take a pin-vise with a #75 drill bit (.021inch) and drill a 1/8 inch deep hole in both pieces of the cut. Insert a piece of .020 brass rod, (available at any LHS) glue with CA and cut the rod to just slightly more than 1/8th inch. Bend the rod with pliers to approximately the desired angle. Put a drop of CA on the other half and push onto the protruding rod. Position the arm, leg, hand or head by rotating or bending the brass rod into the desired position. Fill the gap with putty or gap-filling CA. Use a "Mouse Tail" file to file the seam smooth and paint. This technique will allow you to position arms, legs and heads to virtually any position you want. It may sound like a lot of work, but this is how the pros do it.
P.S.: For really tight spots, break off a short piece of jewler's saw blade and put it in your pin-vise, with the teeth pointing towards the handle, (not more than 1/2 inch long though, the tiny blades break easily). This will give you the smallest saw in the modeling world, great for cutting in places nothing else will fit. But be gentle, cut only on the pull stroke, they will break!