One thing that someone almost touched on but didn't quite elaborate. It sounds like you edited the buildings for a nomad faction. I think the parthians have an internal name as one of the roman factions, they use pastrolism as one of their governments anyway(which the romans don't). If you want to edit the buildings or units or anything for a faction its important to know their internal names. The Romani are 'Seleucid'. So technically the old seleucid faction got reskinned into the romans you see now. make sure you edit that internal faction to change the romans in-game.

I'll post the list because I can't remember where its been posted before:
Game name - Internal name

Rome - seleucid
Saka Rauka - pontus
Arverni - scythia
Saba - saba
Macedon - macedon
Ptolemaioi - numidia
Arche Seleukia - romans_julii
Karthadast - egypt
Parthia - parthia (looks like I was wrong, maybe this whole post was a waste of effort...)
Pontus - carthage
Aedui - gauls
Sweboz - germans
Casse - britons
Hayasdan - romans_scipii
Getai - dacia
Koinon Hellenon - greek_cities
Baktria - romans_brutii
Sauromatae - armenia
Lusotann - spain
Epirus - thrace

Hope this helped at least, even if it doesn't serve the OP much its useful to know.