Just be aware that when deleting OpFor units from the lobby, they won't have checkboxes in the scenario resolution. So if you're expected to "Force withdrawal of 50%" but you've pre-emptively removed 51% of the enemy units, you cannot check off enough to satisfy that condition. You can still set the overall result as "Victory" at the end though.
Another alternative to removing them entirely is to stagger their entry. You might delay entry of the second half a dozen or so rounds to give yourself enough to time to deal with the ones that deploy right away.