what would i have to edit to do this? i want to have 2 versions of NS 3.0F (one custom, one vanilla), and i was wondering how to change what NS is displayed as on the STEAM menu. would it be in the liblist or something? i can't remember...

Open the liblist.gam with a text editor (in the NS directory) and edit the line which starts with "game".

obst ftw, as usual.

when i do this, i can't connect to NS servers... says you're running the wrong game.

so i guess there's no way to do it without forcing consistency errors...?

I do it, and it always worked.
You have to select the right NS in the Steam Filters, then it should work.