So I’m playing through as Zer0 and want to get a Pimpernel at level 72. Am I able to do that mission again on the OP levels or if I get one at 72 will that be the only one I can get out of UVHM?
Yes, you can get it again. Play Captain Scarlett DLC at lvl 72 and then reset UVHM for the OP levels.
This will reset your entire story playthrough, but it will also reset the DLC. You can then just keep farming the DLC at different OP levels.