think you should just put correct entries into "commander_unit_permissions_tables"
there is a "faction_key" (you'll have to track back that specific rebellion faction into "factions_tables")
and a "unit_key" (put the unit_key you want them, found into "land_units_tables")
it's not a short work but there should be everything (if the unit is linked to the faction optherwise you'll have to mod other unit tables I fear)