The extra profile fields being used by some of your hacks in the member profiles may cause a problem. If your UBB does not work after the upgrade, you will need to remove the extra profile fields from the profiles.
As far as I know you cannot revert back to the old scripts after upgrading.
We have not upgraded a board that has had additional Member fields hacked in and are not sure what your results will be. There is a script available at UBBdev that will remove these fields(look in the chit chat forum). I have not used it, cannot tell you how well it works and obviously Infopop cannot support hacks. Be wise and back up your data before you try hacking or unhacking your board.
Correction, and FYI, you can revert back to the old scripts if you need to as long as you have not deleted the original 4 variables files. You may run into a maxmemfields hack alert and will have to adjust that in ubb_library.pl accordingly.