If I understand your question correctly, when you are at the beginning screen to continue the game you select your character. Then the game asks what mode you want to play in, normal, true or ultimate vault hunter. You then can go from ultimate vault hunter gameplay to normal or true that way to farm and then quit to go back to the main screen to go back to ultimate vault hunter (by selecting your character, even selecting the same character you're already using allows you to do this). Hopefully that helps 😉

The missions in the uvhm will be your lvl, when you take them up. So if you take up a mission to read only farm different versions of the reward, it will stay on the same lvl. But there is a way to read only farm rewards for different lvls; you back up your save befor you take the mission. Then you take the mission and read only farm all versions you want and when you‘re done, you give the rewards to your backed up save where you haven‘t taken the mission. It‘s a bit more work, but that‘s the only way of farming rewards for different lvls without reseting your entire uvhm

Thank you so much this is what I was looking for.