I made four more flags for France. Yes it remained outside of the war but the flag still can change.
One is a funny flag that I found about Belgium current situation (not relevant to this topic but I couldn't resist

).
Then, in my opinion, you'll find:
- the flag of Britany (probably semi independent from Paris).
- the Union Corse (combining the flag of Provence with the black head of Corsica)
- two possibilities for the Franco-Belgian Union. I like the one with the rooster of wallony. However, the other one includes the flag of Liège in the French flag. It makes an important statement as most people in the Province of Liège would tell you that their province is the only one and true Belgium. I'm not convinced by this but they have a point: Liège always retained some kind of independence under the rule of its Prince.