Q:

Is there any way to acquire unique guns twice after you've entered Ultimate Vault Hunter Mode?

In Borderlands 2, there are several unique items acquired from certain missions (such as the pistol Law and the shield Order. The stats of those items depend on the level your character is at when he finishes the respective mission. Of course, if you enter True Vault Hunter Mode or Ultimate Vault Hunter Mode you can get them once more since it restarts the game and resets all quests. Right now I'm in True Vault Hunter Mode getting close to finishing the story and entering the Ultimate Mode. But I'm wondering what happens if I finish a quest that awards a unique item then. There's no higher difficulty/mode after UVHM, so no quest reset either. Does that mean that I can get all those unique items just once more in UVHM and then never again? Or is there another way to get them again (except creating a new character, trading or cheating)?
I'm asking because there are some items that I would like to get at max level so that I can use them in endgame combat. If you can indeed get those items only once in UVHM, I would hold out on doing the respective quests until I've reached max level ... 

A:

Indeed it is possible to get these weapons again, which involves resetting the missions. However, it is not possible (without cheating) to reset a single mission; all of them must be reset. Additionally, it is only possible to reset the missions on Ultimate Vault Hunter Mode. 
From this thread:

To do this, at the start screen, select a player. Then when you're asked to select a difficulty to play on, highlight UVHM and it'll give you an option to reset it.

NOTE: Doing this well reset your entire UVHM playthrough, so any progress you have made will go away.
This should allow you to replay the missions that give you the Law and Order items, so you will be able to obtain them at whatever level it is you are at. Additionally, it is also possible to reset UVHM as many times as you like, so don't feel the need to shy away from quests due to a lower level.

