Mod Element: Custom Drops for Blocks and Mobs

This mod element would allow mod creators to add a custom drop to already existing blocks or mobs from vanilla minecraft, or even adding new ones to modded blocks and mobs too. In it, we would have the options to choose if the custom drop would replace the original one or if its additional. Also, we should be able to set the rarity of the drop in a scale from 1-5 (i think it's enough, idk)