How do I set my level, unlocked weapon equip slots and playthrough mode?

With Gibbed's Borderlands 2 Save Game editor, open up the save game file of the character that you would like to edit and make the following changes:

Setting a character's level

In the 'General' tab, type in the level you want the character to be in the 'Experience Level' field, and then click on the 'Sync' button of the 'Experience Points' field to automatically compute the appropriate experience points for that level. Alternatively, you can set your character to match another character's exact experience points by entering the other character's experience points in the 'Experience Points' field and then clicking on the 'Sync' button of the 'Experience Level' field.

Unlock all 4 weapon equip slots

• Go to the 'Bank' tab, then click on the 'New Item' button.
• In Type, select GD_StorageDeckUpgrade.A_Item.INV_SDU_WeaponEquipSlot (near the bottom of the list).
• In Balance, select: GD_ItemGrades.StorageDeckUpgrades.ItemGrade_SDU_WeaponEquipSlot
• In Manufacturer, select: GD_Manufacturers.Manufacturers.Stock
• Keep the rest of the fields untouched.
• Right-click the created item and then select 'Duplicate', to add a total of two SDUs (Storage Deck Upgrades; to unlock the remaining locked two weapon equip slots).

Then, in the game, go to the Bank and retrieve the Weapon Equip Slot SDUs. Retrieving an SDU will unlock a weapon equip slot. The SDUs won't appear in your inventory. Note that in True / Ultimate Vault Hunter Mode, you can access the Bank near the start of the game at Claptrap's Place, Windshear Waste.

Unlock True Vault Hunter Mode (TVHM) or Ultimate Vault Hunter Mode (UVHM)

For TVHM, go to the 'Raw' tab and set PlaythroughsCompleted to 1. For UVHM, set PlaythroughsCompleted to 2, and set LastPlaythroughNumber to 1.