For example you select a block in your hotbar and point and click a button at an already-built build, and it changes every adjoining block of the same type to the block of your choice. The blocks you replaced would drop near you and the blocks you replaced them with would be depleted from your inventory. It would ONLY affect adjoining blocks tho, not every block of the same type. It would only replace as many blocks as you have in the selected hotbar slot to begin with. I think this could be used in survival and creative as a way to quickly change build color palletes without tearing a whole build down and rebuilding.