I was playing Borderlands 2 with my friend last night and he downloaded a save that had all the pearlescent weapons and he said he had over 2000 slots available in his backpack. I asked him exactly what it said and my friend told me it said 83/2500... I modded and gave myself all the weapons, so now my backpack is 83/33... So I can't pick anything up in my backpack... How could you still mod your inventory??
if you mean you want empty slots to pick more stuff up then you can't, gearbox patched it a while ago, all you can do is overfill it with the editor. What iv done to get around it in the past is overfill the backpack with say for example 400 of the same pistol then always keep one of them equipped then when i find an item swap it with one of the pistols so really i treat the pistols as empty slots.
if you have gibbed's save editor you can set your blacklist upgrades to 0 and buy them again in the collection the last 2 numbers are you backpack and your bank upgrades