Do you mean adding a column to view the version of the ID3 tag along with the Artist, Title, etc? If you’re looking for something that does this, then you should check out that MP3Tag program I posted about above. It has such a column in its interface, and tracks are sortable by any of the column headings so you could order them by ID3 tag version and know just which tracks to modify. MP3Tag will by default save in ID3 v2.3 (I believe), so highlighting tracks without an MP3Tag (or ones with ID3 v1 tags) and clicking the Save button should automatically convert the tag to ID3v2.
One thing to watch out for, before you go saving any changes, is the values in the Artist, Title, etc. boxes on the left side of the MP3Tag window. If you’re doing a bulk conversion of several hundred tracks, you want to make sure that the values in each of these boxes are set to “Keep” (this option can be selected from a drop-down menu). I’ve found that sometimes, when holding down Ctrl or Shift and selecting a number of tracks, sometimes the boxes on the left are populated with the information from the last track clicked. You don’t want to go updating a few hundred tracks and name them all the same, that would be a nightmare to fix later on. Not that I know from experience, or anything…
Oh, one other thing… Do you have your iTunes automatically keep your files organized by the ID3 tags? The option for this is called “Keep iTunes Music Folder organized”, and it’s in the “Advanced” area in the preferences (at least on iTunes for Mac OS). Just to be safe, I would delete everything from your iTunes music library (making sure not to answer “Yes” when it asks you if you want to move the songs to the Trash), and then reimport your library once you’re done editing the tags. The only reason I say this is because I don’t know what effect editing the tags will have on your iTunes library. It might just edit the files back with the information from your library (artist names, song titles, etc.), negating all the work you just did modifying the tags! That would be pretty frustrating.