Not just the civil war, but Victor Napoleon Bonaparte's[1] coup and conquests after the the restoration of the Kingdom. The Greater French Empire, or 'Unitary Republic' as they called it,[2] only just collapsed twenty years ago after all, and the French are still keeping as tight a hold on the Rheinland as they can, despite the German Republican Army's attempts to drive them out. [3]With a French intervention, a rebel victory and French economy falling down, perhaps the nobility and clergy won't take arms against Louis XVI reforms, seeing some Enlightment ideas might work ? There would tensions, obviously, concerning the privilèges, but the Civil War could be avoided.
OOC:
1: TTL's son of Napoleon, Napoleon himself remaining a distinguished officer in the Armee Royale in TTL.
2: Seeing as I'd most likely be a Brit in this timeline, I'd call any super French state a derogatory name.
3: The GRA being an obvious reference to the IRA.