I don't know if changing the limbs would be cost effective since it is not something that is normally done. You might be better trading in the newbow for one with a lower draw weight (when the time comes). Also, shooting may help keep those muscles healthy and you may shoot that bow for longer than you think. If you get a 50-60# now, that would give you the 60# right now (maybe even a little more) and then you can take that all the way down to 50# as needed.