Thanks for the reply!
There are no "sumpf" files that are script files, but the only other files I found that might be relevent are '_zm_perk_random.gsc' and '_zm_perks.gsc'. The former seems to exclusively deals with the Wunderfizz, but the latter seems to deal with perk machine locations and randomized spawns.
I've been trying to print contents of things to find out what to change, but it seems to always throw an error or just not print, since I don't really know the structure of the objects whose content I'm trying to print.
So I'm pretty confused and stuck. I might just give up soon unless someone would know exactly what to change for this.