The Byzantines are not the only civ in this modmod that winds up with a name that the contemporaneous people did not use for themselves. I don't mean to open a rabbit hole since the nomenclature of the Byzantines is a real locus of attention in the historical strategy community, but at least to me this modmod clearly uses the widespread English names for the states. Germany is Germany and not Deutschland, Japan is not Nippon, China is not Zhongguo, etc.
Also, there is already a dynamic name switch for the Byzzies when they reconquer Rome that turns them to the Roman Empire, which I think is sufficient.