How do I replace an item when right clicking with it?

So, I've been trying to make a procedure which replaces a certain item with 4 of a different item when you right click on a block with the item.
I've been trying lots of different things, and they haven't been working out for me. The closest I can get is exactly what I want but it replaces the first of that item in my hotbar or inventory.
I need to know if there's a way to do this (and there probably is).