If rhe figure is glued heavily or thick- drill or punch holes under the shoulder about mid to high lat on the seam line. Boil tje figure in 45 second intervals. Use an awl if possible to push into the hole. One side. Then the other. Slowly do this. If you see lifting or warping of the plastic, stop, repeat the boiling process, then continue. The heat loosens the glue and keeps the figure from cracking.. Be sure to use tongs or similar to hold the torso so it doesn't touch the bottom of the pot. Pat dry between boiling to avoid burning yourself on with the water stuck in the joints while working. If you must use a razor, this will also make it easier as the plastic is more pliable and the glue is loosened. This process is extremely beneficial for large and hard to crack torso or parts in general.
If you are working with staction figures, it is much easier to boil between cutting.
For Sota figures- the torsos are solid rubber or larger ones, a weird plastic. Boil and push the rod through using an awl or small screwdriver. The joints on a Sota figure are boil and pop.
Mattel Elite-drill and boil as in the first example.
To avoid tearing on boil and pop joints as the may get soft- get a string/dental floss. Wrap it over the shoulder so it is between that and the torso. Use that so that when you pull it comes straight out and avoids tearing the joint. You can also use a twisty tie and twist it around the inside of the joint and pull. Another method is to wrap the string around a screw driver clamp the figure down and twist the screwdriver until the slack is taken up and the joint will eventually be pulled out.
If you've already applied sculpt to a piece- it is best to use a blow dryer or dry heat to attempt to remove parts. Some smaller details may be loosened by boiling and the sculpt will eventually break off.