Infinite play throughs, Backpack SDUs, skill points
This is save corruption. I take no responsibility for anything that goes wrong attempting this and you are probably an idiot for trying it.
If you would like to perform this trick there are a few things you need to prep. First you will need two characters on you hard drive. One character should be your primary character that you plan to use and the other one you have prepped to transfer what all you want onto your primary. The second thing you will need is a friend on a LAN or the internet to allow you to do this save corruption. When prepping your character you need to take into consideration what all will be transferred.
You will get the fast travel locations, audio logs, quest data, level (temporarily~~ I'll explain),gun proficiency and play throughs of your secondary character transferred to your primary. With this in mind you should unlock play through 2 but ignore every claptrap rescue quest in play through 1. Complete play through 2 with all the quests you want to be done completed and those you would like to be able to redo not done.
Once your secondary character has been created and prepped the process to transfer that data is actually remarkably easy. You need to have your friend start a private online game and remain in the pregame lobby. Have him send you an invite to join his game. Load your primary character and select ready. Now here's where the timing bit comes into it. Your friend will need to start the game at roughly the same time as you select a new character. If you timed it correctly you will be able to change your character during or after the load screen. Change to the secondary character and then save and quit. The next time you load your primary character you will have the stuff I listed above transferred over. When I said your levels will temporarily be lowered what I meant is that the instant you load that save you will gain your original level and this can be used to your advantage. If your primary character was level 56 and your secondary was level 30 you would regain 26 levels instantly. Those levels would give you an additional 26 skill points to use making you skill points that of a level 82 character.
If you have anything to add feel free.
People think it must be fun to be a super genius, but they don't realize how hard it is to put up with all the idiots in the world. - Calvin & Hobbes