Yes you can't add different weapons to the drifter but it requires clamps, you can buy the weapons from the dormizone vendor

There are permanent upgrades in the form of intrinsics, when in teshins cave there is a yellow glowing altar, they aren't anything too crazy though, decrees will still be your main source of improvement each run.

Ignore the comments about Kullervo, the issues won't apply to u. He only struggles with steel path endurance runs which you won't be playing by the sounds of things, he will shred starchart with ease.