Hello,
I would rather modify the wind velocity just after the reading of your wind file in lecdoi.f and noudon.f (if the wind evolves in time) or lecdon.f (if it does not evolve) or in venuti.f if you have a user-defined wind file format. You could also apply the coefficient to the wind velocity in the routine where lecdoi/noudon or lecdon or venuti are called (condiw.f for lecdoi and lecdon, semimp.f and cormar.f for noudon...).
Regards,
Elodie