Can The "forbidden Six" be used as Mounts?

[macsen rufus]

So new factions can't own units using these 7 bifs. Can a workaround be to just not give them such units?
But then hiring a mercenary can cause a crash? Not using these bifs would reduce the spots for new models(50 folders in total).

It's not so much 'new' factions per se, it's factions beyond the 20th. If you only have 20 factions, all will be well And there is no workaround, if such a faction uses one of those BIFs you'll get a CTD going into battle - whether it's trained, hired as a mercenary, or bribed.
You HAVE to chose - limit your factions or limit your BIFs - those are the only options (hence the joy when we started to get 640x640s working )