RE: What to do with the spare limb?
If you don't have a backup bow, I'd recommend keeping it. According to Bob Ragsdale (a very knowledgable archery engineer), you can get any bow to shoot perfectly by adjusting tiller and nocking point. I remember reading where he once said that you could put a 60 lb and 70 lb limb on the same bow and get it to shoot perfectly. I believe him.