Here's the internal faction names:
seleucid - Romani
greek_cities - Koinon Hellenon
thrace - Epeiros
macedon - Makedonia
numidia - Ptolemaioi
romans_julii - Arche Seleukeia
romans_brutii - Baktria
romans_scipii - Hayasdan
carthage - Pontos
pontus - Saka Rauka
armenia - Sauromatae
parthia - Pahlava
dacia - Getai
germans - Sweboz
scythia - Arverni
gauls - Aedui
britons - Casse
spain - Lusotannan
egypt - Qarthadastim
saba - Saba


As far as I know you can't copy/paste directly into the game.

Also I find it a bit funny that you chose to use Saba as an example since it is the only faction who's faction was renamed.