RTF is a global modification that replaces all towns in the game.

If I understand correctly, the animation file in Heroes is just a skeleton with movements, meaning the animation file doesn't need a model, right?

Not exactly, since the game uses animations in the Granny format, it is indirectly linked to the skeleton... and in some cases, the skeleton file (which is also in Granny format) can be changed... unfortunately, it rarely produces a good result; usually, there's always some distortion in the output, but this isn't due to Granny, but rather to the creators of the models/animations not adhering to the principles of universality (at one time, a respected person tried to explain to me why this game produces such results, but I don't remember the details anymore), although perhaps they didn't even have that goal, as they were creating them specifically for a particular model of a particular creature/character!