Adi
If i pit in late on in the race, for an harder compound tyre than what i am using, and before i pit in, i reduce the fuel load by a few litres to reduce number of laps, can the amount of fuel in my car be reduced to what i want, or do i have to compensate?
I'm not sure I understood the question.
Fuel reduction = Lap reduction. Whatever changes you make on-the-fly during live races, they get transfer to the car. You do however have to manage fuel as consumption will fluctuate based on PL. Always good to check a lap before pitting to make sure your fuel matches your laps for the next stint. Of course, never leave a lap count at .0 ei;(5.0,15.0,...etc..) to minimize your chances of running out of fuel.
I hope I'm on the right track here in relation to your question.