Help w/ code for next mod update!

Hey everyone, you might know me for my semi-popular mod Tools+, Well I need to do one last thing of coding help before I can finally release the next update. I need a way to make it where when you use a special pickaxe of mine, you will receive a different block/item then you would normally get. Like say I break a piece of stone with this special pick of mine, and I receive mossy cobblestone instead of regular cobblestone, and also if there is a way to get multiple at once like breaking coal ore and getting back 3 coal instead of just one.
Please if anyone can help this is the last thing I need in order for me to release my next update and I will credit you if you do help me.
Thanx, Syliris