Apply an effect to a creature via animation.

So, I think I've figured that out, but can I save the model separately from the creature? As far as I know, I need to delve into the map files, but I'm not sure exactly how, and another question: to change the appearance of an artifact or creature, for example, its thickness, or make it hook-shaped, or separate the shoes, do I need to modify the model itself, right?

I also had an idea: take a creature model and separately cut off parts of its body, for example, arms with armor, and make them as separate creatures or dummies, or is there another way?

And I assume that with each animation, I need to do some tweaking, or can I just attach it to a bone?

I would also like to know what the Custom value means and what it is used for?