Graygores zealous shortbow question

I noticed theres an open upgrade slot in the grip of this bow...can i add a grip upgrade? any help appreciated thnx

That's a green weapon right?

You can't mod green's unfortunately. So if it is missing a mod, that's the way it will always be.

every green item has the maximum number of mods. Graygores zealous shortbow has the zealous and defense mods.

see the "Armor +5" part? yeah... that's the grip