hi... In the trainer its the same option...
Go to ship
ALT Tab out
Change your backpak size in trainer. It will effects your vault that is open
Close Vault and re open it...Now you can see the added space.
Now you swap to the backpack via vault menu
And redo the same steps
Hope this helps
That happened to me as well.
I was looking forward to something like this too... I used a CE table to do this on the older games, but figured by now that functionality would be included in a trainer at this point. I did note the loot rarity chance, but activating that hasn't done much for me at this point, nor has using the editor to boost the value to astronomical proportions. I know it'll take quite a bit more scripting to map guaranteed rarity drop rates/items, and depending on the coding it might not even be a possibility for this game. I'm remaining hopeful though, after the 3rd-4th playthrough it'd be nice to maximize the number of legendary gear drops you get to ease through the game...
Yeah I'm really hoping it can be done. I haven't beat the game yet so I can't test the guardian stats, have you tried putting the luck in the guardian stats really high?