You are more than welcome to change countries mid-way. If Parthia becomes independent, I can reserve the spot for you, if this game starts. In the cited game, I started as Rome, then left and rejoined later on as the Achaean League, which I eventually defeated Epirus and Macedon, and changed into the Hellenic Federation, right before the GM declared the end of that version's game. So changing sides is not frowned upon if you have a reason to.
EDIT: Sent a PM to Ludens. :)
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