Q: Why can you only 'commit' a classifier once?

A:  When you 'commit' a classifer, the following take place:

• ForScore scans results and determines what classification each guy's score represents.
• If someone has not reached a higher classification, data is processed normally.
• If he has reached a higher classification
• The master shooter database is updated with his new classification. For any subsequent matches, he will automatically be registered with his new classification.
• The registration 'snapshot' for this match is updated, so the match results will list him in his new classification
• The match results will show this shooter's classification was 'Previously XYZ'.
   Here's an example.  (You can disable this feature in Program Preferences if you wish.)
• The match is marked as 'committed' and the Commit Classifier button is disabled on the match data entry screen.

My intention was that this procedure only be performed once for a specific match, after all scores have been entered.  I didn't provide functionality for the procedure to be invoked multiple times (in which case it would need to ignore guys whose classifications have already been changed in this match).  Nor did I provide the ability to go back into the shooters and matches databases and undo the changes that have been made.

So as with any other one-way process (like 'pruning' a match), I suggest that you back up your data files first so you can revert if you don't like the result or if you need to correct an error and recalculate.
The Data File Backup option on the File menu offers a quick backup...   but it will only keep one copy of files (shooter, match, guns, event) that are copied into the
   c:\program files\forscore\backup folder.

If you want to keep more backups, you'll need to manage that yourself.
The Data File Archive wizard from the File menu can be used to create a zip file containing your data. The zip file can be unpacked with WinZip® or any other zip file utility.
Of course, this discussion is a good time to encourage you to use the Data File Archive wizard or another means to back up your data to a CD-R or flash drive or some other medium as well.