I just made a copy of"iTunes Library.itl" before the I installed the ringtones. If I want them gone I just replace the current file with this copy and delete the ringtones in the ringtone folder, it works great. You'll need to update the file if you make any changes in iTunes though (add music or movies).
I tried rebuilding the library once via the Apple instructions but it erased all my album art. That took awhile to re-install. YMMV