it's an all or nothing option (control units)
when you turn it on and then move over the enemy units, they turn green underneath (indicating they've been 'converted')
once converted they are converted for the duration.
turning the option off just makes it where mousing over them does not do this any longer- however any units that have already been converted remain so-
best,
Cal
Thanks Caliber for info,
I replayed the level from the begining because i pushed Control unit button by mistake ..