I have old galvanized pipes and old supply valves under my sink. I needed to shut them off and turn them back on, and they started leaking, as they do. I went to the store and bought replacement valves, but I just could NOT remove the old ones. They wouldn't budge, and the Internet wisdom says to not DIY with old galvanized pipes. So instead, I took apart my brand new valves, and replaced only the turney-part. Not sure what that part is called. It fixed the leak but I want to know if what I did was okay.
Reason I ask is that I couldn't find only the handle replacement part at the store, it's sold as a whole assembly. I figured if this part is okay to replace ad-hoc, then it would have been sold that way. It made me think twice now.