Is it possible to adjust setup values like the diff lock, brake pressure and front and rear wing angles so that I dont need to be going in and out of the track only to try different setups or minor changes?
Brake pressure can be altered on-track. don't think much else on your list is, but it wont hurt to check controls, you need to set buttons for brake pressure there anyways.
I've triple checked all controls and in the rFactor "as is" you can't change what I want (have to check the pressure, I've only seen the brake balance). What about something like a mod? Would that be possible, or is there any mod that allows that kind of value changes?
No, the in-car adjustments are limited and have to be enabled by the mod (vehicle). Brake bias, front and rear antiroll bars is about it for actual setup adjustment. Depending on the mod you may be able to adjust the rev limiter via boost and even adjust some of the aids (like traction control) but obviously that's not really setup testing and is very mod dependent regarding actual effects. Ultimately this is a sim, and most cars don't allow you to adjust setup on the fly. Still a bit easier than real life because you can escape to the pits whenever you like (in some ways this is similar to asking for a setup testing mode where the game puts you out on the track immediately, with tyres, brakes etc all up to temperature so you can drive around a few corners and judge your setup changes, rather than having to actually drive a lap or two to warm everything up first. Technically that would be possible (for ISI) but as a design choice, for a sim, it's not a realistic option)
