Lavaliering is a big deal - at my school it was like being "engaged to be engaged". Pinning is extremely rare.
My husband, an independent, "lavaliered" me with a little heart pendant. My sorority held a candle pass just the same as if I'd been lavaliered by a fraternity member.
I've never heard of a restriction that a girl can only be lavaliered once or that a guy can only lavalier a girl once. If the relationship ends, I don't see any reason why the girl can't accept a lavalier from a new boyfriend or the guy can't lavalier a new girlfriend. Still, a couple should consider lavaliering/pinning very carefully, as it is sort of a pre-engagement.