is there a way to switch factions, midgame?

[MajorFreak]

nt.

[Simetrical]

You can use a script and the "control" console command (which doesn't work from the actual console, only the scripting console_command command). I believe there's a scripting tutorial in the Guides, Tutorials, and Tools section (https://forums.totalwar.org/vb/forumdisplay.php?f=77) somewhere.

-Simetrical