the way to fix it is uninstall the MOD or whatever you did then make a new profile that has absolutely no save game data on it. I tried doing MP on my ARC mod profile and the DC-17 were replaced with DC-15s and the helmets were clone helmets on commando bodies (pretty awesome still trying to do it without it glitching.) so I made a NEW one for MP only and it worked just fine.
"We were used and betrayed by the Republic we served. I will protect my brothers to give them a future. I don't care who I have to kill to get them out. Republic or Seperatist, I only have one order. Kill them all" - Baron Commando 'Dax'