Hi Leo,
I emphasise that I'm not familiar with the F70 / F100 or their engines, so this comes from general principals. Taking apart your post, quote by quote -
QUOTE - "Once you get these new V1 and Vr values, you still need to check them versus your runway performance tables ( for any given or individual airport) right? If you find a lower V1 for the actual temperature and actual weight, then you cant flex at all".
No, you can't flex here, because individual runway analysis (I assume you're referring to RTOWs) has established that you're Accelerate-Stop limited for that runway, and raising V1 would be out of the question.
QUOTE - "But this can only be a problem when field lenght is limiting factor".
Yes, specifically the ASDA (Accelerate-Stop Distance Available) is limiting. Don't forget that TODA may be much longer than ASDA.
QUOTE - "The lowest V1 found is still ruling isnt it?"
Ruling in the sense that it will govern whether you conduct a normal or a flex thrust takeoff.
QUOTE - "Now i have a look into the runway table and find lower speeds for V1 and Vr at 50°OAT or assumed OAT.........Which V1 shall i take then?
An RTOW arising from a specific runway analysis has already considered all implications for that runway. Unless your instruction to adjust V1/Vr applies in ALL circumstances, my feeling is to go with the RTOW speeds.
QUOTE - "Is it right that flexing below 30°C is not allowed because it is the flat rated temperature?"
I don't know your engine, but if, as I suspect, 30° is the upper limit of the flat rating, it would be pointless to flex to a temperature below 30°, the engine would be delivering full thrust.
Again, I emphasise that I'm not familiar with the F70 / F100 or their engines, take this as general information, there may be flaws in my understanding.