Prevent the use of a GUI slot under certain conditions?

sorry for wrong translate (google translate)

hello i'm asking for help on this forum for a procedure that i can't do. it would be to prevent the use of a GUI slot under certain condition, condition which would be the content of a variable number.

I've created a consumable that when used adds +1 to a variable but, the idea is simple + you eat this item more a bag added in my mod has usable slot.

I've managed to block the fact that the item can be removed once the liver has been put in, but I can't figure out what the procedure should contain as a dependency to do the opposite as well, i.e. prevent an item from being put in the slot if the variable doesn't have the right number.