Thanks for clarifying that. Didn't know about the Mac.
This works enough, but not perfectly. Perhaps some of the images vary slightly in size. Trying to put the blue human image on the mean looking dark cat, you can get the main image on the party and training panels to work. Also the unarmed animations seem to work (I may not have tested all), but the sword and bow don't. Didn't have a pole arm to test that.
Each character seems to have 21 images - the main full color image and five animations each for unarmed, sword, bow and pole. I think they are for standing, attacking, defending, casting and dying. To put the blue robed male human on the dark colored mean cat copy these bmp files: G226, G2800, G2802, G2803, G2804, G2805 and rename them to G238, G3400, G3402, G3403, G3404, G3405.
This makes a robed human that turns into a cat if he picks up a weapon, which, for me, is quite acceptable in roleplay terms.
[edit]The animation changes may only work for a few images. Looking at images sizes, there appears to be quite a range. It was just luck for me that the robed human matched part of the cat image set. The large portraits do seem to be interchangable, though.