What about using createUnit and deleteVehicle to do that.
If you want resistance to start friendly to east, this can be
done as suggested above (may it be editing mission.sqm,
or let them start grouped to an EAST leader).
Once you want them to change sides, just deleteVehicle
'em all and createUnit another bunch of resistance soldiers.
Therefore you could have some dummy WEST guys somewhere far off the battlefield, to let the new units join them.
If you want them to switch sides more than once, you could
use the same technique again, but you would need also some
dummy EAST units for that.
~S~ CD