I'm using the KSmod scenario generator and i was wondering if it was possible to keep the losses in an OOB after a battle, in order to use it in a future encounter?
It's definitely possible. The scenario system is designed to carryover battle results from one to the next. As far as whats involved, take a look at some of the carryover scenario series from GB. There was a Kershaw series I posted and I believe an AP Hill as well. It involves editing the scenario.ini file to include the carryover=1 line, as well as indicating the scenario carrying over from.