As the title says, I'm looking for tutorials about how to modify the appearance of an object, not a recolor, but a completely new appearance.
I've tried some tutorials before, but I'm having trouble creating the mask with 16 bits image

By the way, I'd tried the tutorial by Woobsha (you can call me stupid if you want)
but, I don't know if it's because the version of the program, he/she used is very old or what, but I couldn't make it

Try Bunny Wuffles' tutorials. Her site is down, so they're hosted by Woobsha, but they weren't written by Woobsha; they're just preserving her stuff.

Thanks!!