I would like to clear the Chernebog system to get the rewards (influence). But the system is too low for my character. Is there a way to change the difficulty of the game?? I can do it for story levels, but not regular ones.
Killyox is right, but if you want to be sure of staying in the same system you can run tarot missions. They're ALWAYS in whatever system you're currently parked in. Obviously, that's not the easiest or most efficient way of doing things, but there you have it.
The only way to get more difficult missions, is to do the very low level ones, hoping that a new one with higher PR appears.
What you can do, is go to that system, teleport back to command center and then launch a priority mission, it's not 100% relaible, but I noticed that often, the priority mission takes place in the system you were before launching it. And you can change difficulty in priority mission to get some glory out of it.