Originally Posted by MKE-MR

Your best bet is to check up front for availability a few dates around your booked date. If it looks wide open, it's at least somewhat helpful to your chances of changing later.

In my recent RTW, I had one segment which I couldn't book on my preferred date. About two months later it opened up and I changed it, and two segments around it, to fit. No issues at all. Another segment, I got the only D seat within weeks, and in watching availability for the next three months, none ever opened up on any alternate date within a week of my booked date. I would have been stranded for a long time had I needed to change.