Forcing Yuezhi to invade anyway + adding units

[bovi]

You need to do loads of stuff to get a unit to work for other factions that they are set up for, including changes in EDU, EDB, DMB. Possibly others. Any mistake you make will likely not give any warning but will rather crash the game at a later point. If you really want to do this, you need to research the dependencies.

[Connacht]

You need to do loads of stuff to get a unit to work for other factions that they are set up for, including changes in EDU, EDB, DMB. Possibly others. Any mistake you make will likely not give any warning but will rather crash the game at a later point. If you really want to do this, you need to research the dependencies.

So, I suppose I should stay quiet with my hands, otherwise I could risk to muddle everything and get frequent CTDs.
However, I wanted to recruit units like Armenian light spearmen or Arabian archer-spearmen with other Mid-East factions (i.e. Pontus or Seleucians) and not only with respectively Hayasdan and Sabaeans.

[Tellos Athenaios]

At least as far as the Seleukid case goes:
In the case of the Armenians: should be farily easy to mod in.
In case of the Sabaeans... not that easily done. You see the Sabeans are on their own texture and that's not the merc one; but the model is also used for the Eranshar archer guys (who occupy both romans_julii and merc slots)

Though I dunno, perhaps the Slave faction has it's own model, you can check that with the EDU. If so you can try to award the romans_julii a slot on the slave model also. But only if the slave's don't happen to recruit the merc Eranshar guys. And I would count on that to spoil your fun.