Hi,

i just wonder if i can name an side's lvl let's say veh.lvl, but put in some sides/vehicles/weapons that do not start with veh, but with rep and cis??

Yep, the *.lvl name is derived from a level *.req name and that is all. The contents of the *.req are unrelated to this.
Most of what you see in the Modtools was done for organizational purposes by the devs.

sounds great, so i can put all vehicles in an side named veh, but the vehicles can be named rep or cis

Thank you