Title says it all, I'm making a modpack and morphlings can change their size. I'm going to modify this mod to allow me to make it so only players with the attribute of morphling can access it. Would be great if you could make it a feature so I don't have to add it to a datapack for the modpack when it comes out.

Hello there I'm actually working on a mod like this right now I'm making a shapshifting origin so you can turn into animals and other people

You don't need any sort of mod change to allow this, as you can just use the /identity command. For example, /identity equip @s minecraft:bat will change the player into a bat, even without needing to unlock it first.