Depends on what the change is, for me. I'm not okay with changing things that would alter the plot. If a character died, for instance, I wouldn't go back and change it so that they lived. That's a rather extreme example, though.
I'm okay with fixing typos, rewording for clarity, correcting inaccurate descriptions, and resolving continuity errors. Anything that is clearly a "mistake," I want fixed, but things that are just "inconvenient" for the direction I want to go, I will deal with (work around them if possible, go a different direction if not--both important options for provoking creative thought, I think).
All that being said, I try quite hard and plan pretty extensively in order to avoid having to do such things. I just don't want to turn a blind eye to them if they do end up happening.