I do this all the time too, the only drawback I can tell is they seem to dry up faster after the recharge. Still getting SAME RH for most part though. So I got a 12 pack and just rotate.
That would mean that "re-charged" humidity escapes the humi faster than "new" humidity or that a new pack works slower than a re-charged pack. The new ones do feel different from re-charged ones, though.
__________________ "Man's mind is his basic tool of survival. Life is given to him, survival is not." -John Galt