Texture Variation, Animation Changes and AI Changes

Hello! Uh, this one's a quadruple inquiry, so please answer by starting with the corresponding numbers:

1- How do I make it so a mob spawns with a randomized texture? Like with Horses, Tropical fish, etc. (And if there's a way to change the glow texture aswell with this).

2- How do I make it so, when chasing a mob/player, a mob changes its animation?

3- There's one mob (that applies for all these) that I wish for it to de-aggro and ascend (it's a flying mob) before despawning when its daytime. Is there any way to achieve this, or something functionally similar?

4- Is there any way of modifying vanilla mobs in any way making use of MCreator? Such as textures, sounds, etc.