How do I make mobs persistent with procedures?

I'm trying to make a mob that becomes persistent once you feed it, similar to how sheep and cows work. I don't want them to be tamed because they're livestock, and taming doesn't make them persistent anyways. Changing PersistenceRequired to true using data logic NBT tag does not work because it uses different NBTs from vanilla and is separate when you look in the /data of the mob.

Any solutions?