converting old electric range to gas range, and need a standard 110V outlet - can I re-configure the existing 220V outlet and existing wiring, replacing only outlet and breaker in a legal (code compliant) manner?
Yes. Due to the wire size you will likely need to pig tail (with appropriately sized wire nuts in both locations) to fit into the new breaker (20 amp) and outlet. Since you'll be removing a 2 pole breaker and replacing it with a single pole breaker, you'll have an exposed slot in your cover plate on the panel. Some ppl around here suggest putting in a "spare" breaker to fill the hole, but you can also buy an insert to "plug the slot".
EDIT: Just saw "NoSparksPlease" comment and agree. Let's get a peek at the boxes before we go too hog wild here.