This is a problem Finale users have to work around since the beginning. Let's say you make a measure or a multi-measure rest wider (by dragging its handle or in the measure attributes dialog/measure width setting. When automatic music spacing is turned on in the edit preferences, Finale will automatically erase all manually adjusted measure widths. That's just terrible for so many reasons.
1. You send your Finale file to someone who opens it with automatic music spacing turned on and who then performs the music spacing function for what ever reason. All the measure width adjustments you made will be gone.
2. The only workaround to preserve user made measure width changes is by always have automatic music spacing turned off. This is very inconvenient because you will have to always make sure you only select the music you need to space and then manually force spacing.
3. It is one more thing you constantly have to do to make the music look right.
What makemusic could do to get rid of the problem is simply adding a new music spacing preference that can be checked reading as follows:
INCORPORATE (or keep) MANUAL MEASURE WIDTH ADJUSTMENTS WHEN RE-SPACING THE MUSIC
I reported this issue to the finale support team, but as everyone knows, they will only move on this when lots of us complain about this problem. So all you professional music engravers using Finale, please write them about this problem!