is it possible to modify to make cars change gears at max rev, rather than its usual half rev?
I don't think that's possible, that doesn't ring a bell.
I suppose you had a look at the first lines of the "START OF MECHANICS" part:
START OF MECHANICS STUFF version 1 0.500000 // Minimum turning circle. 1.000000 // Brake multiplier. 1.000000 // Braking strength multiplier. 6 // Number of gears. 200.0000 // Speed at red line in highest gear. 5.000000 // Acceleration in highest gear (m/s^2) i.e. engine strength.
Maybe by tweaking some of these values you could kinda fake what you want to achieve. Didn't see anything related to gears/speed in GENERAL.TXT.