[Solved] required-after can be optional?

I'm working on adding compatibility with other mods in my mod, but I need to wait until this mods register their items and blocks so I can interact with them later.

Would there be a way to make that using required-after, or I should move and register my items on the init, or post init?

PS: The question is, so my mod doesn't say X mod is needed, it's really not, but if X mod is present, then I want to add compatibility for it.