A few Mods have the command "nextlevel=X" (or a command equivalent to that) which will do just what you're wanting. It will tell FPSC to use "X" as the next level. "X" is the number of the level, not the name, btw.
PB has this command, and I believe RPGMod has a command equivalent to it. Just a bit of explanation on the different between the two, though. PB will revert "repeated" levels back to their original states when revisited, while RPGMod will keep the levels in the condition they were in when the player left. So, whichever method is right for you, there's which Mod to go with.
The one and only,
Only those who sow the seeds of their desires will reap their benefits later.
However, I have seeds of my own to tend to. I don't have time to be someone else's watering can.