Hi! I've tried some mods and noticed, there's no even opportunity to fly when you're using mobs from other mods. For example, crows from "Alex's mobs" can't even fly. I know, you can't add every mod on the Earth :)
But is that possible to add aт ability to add/ edit features for modified/new creatures?

Yeah, it is possible to edit mobs which are able to fly via Datapacks.
Here's the wiki page: https://github.com/ToCraft/woodwalkers-mod/wiki/Datapacks.
In case you're not familiar with datapacks, take a look at the official minecraft wiki or watch some YouTube video how to create a custom one.

If you're patient and interested, you could also write me a list of modded mobs and what players morphed as such should be able to do, and I'll try to implement those into the next Woodwalkers-Version. Those two wiki pages show what mob abilities are available right now:
https://github.com/ToCraft/woodwalkers-mod/wiki/Datapacks
https://github.com/ToCraft/woodwalkers-mod/wiki/Abilities
but again, this is completely voluntary and don’t feel pressured to do anything. :D

EDIT: Here's an example Datapack for the Woodwalkers-mod: unlockVillagerTraderBoss.zip

maybe someday you should make a gui like ichuns