Notepad. Yeah.
What DP said is the right process, but because 3ds Max is unreliable with KOTOR models that can cause some serious annoyances - one of the big problems is when you get a difference between what the game thinks is the pivot point and what your modeling program thinks is the pivot point, which skins are especially susceptible to. One particular failure of mine resulted in an eternally sad Malak. Rather than mess about with that, I find it easier to edit the ASCII file directly so you get a model that imports with most things working properly. That minimizes all the fussing around in the hierarchy too. Here is my procedure:
Open your head from Game A ASCII in Notepad.
Copy all the visible geometry from it (head and tongue skins, eye and teeth meshes, plus any extras like hair dangly meshes).
Get a similar head from Game B. Remove all the visible geometry (same stuff as above). Export an ASCII file.
Copy the geometry from step 2 to the ASCII from step 3 in Notepad.
Use find and replace to make sure everything is parented to the right stuff (replacing the first model's name with the second's).
Import into 3ds Max.
Using the original head as a reference, make sure all the geometry is in the correct position. It seems that anything without a skin modifier won't necessarily go in place; for example, Malaks's eyes and teeth had to be moved. I usually look at the XYZ values and enter them, but if you want to mess around with the hierarchy you could delete them, import them from the original game ASCII, and put them back in place.
Rename your model how you want it for the final time.
Export.
Convert to binary.