Also welcome to flyertalk!

It depends on the program you are using how flexible your ticket is and how much it costs to change.
Keep in mind that you need to have award space on the new flight, which can be difficult especially on a short notice. So it often sounds easier to change an award ticket that it actually is. It depends much on the route.

If flexibility is most important you should look at other inexpensive ways to travel. Loock at the paid RTW tickets which book in a higher class, so much less problems to find space.