OK, so, TLDR; yes, it's configurable. I had to press ADJUST on the service remote app to enter an adjustment list menu, and then I was able to change the Area Option to 3122. Then I pressed IN STOP to reset the TV, which allowed me to initialize it for my current location in France, and to configure local French apps, like the Canal+ app.
Rest of story: I wanted to be able to install the Canal+ app because, from the Orange decoder, closed captions don't work. With the Canal+ app on the TV itself, they do.
Other part of the story: Before finding the ADJUST menu, I had exited with IN STOP (thinking it would just exit the service menu) and ended up resetting the TV to US defaults... but this resulted in the region being locked to AUTO OTHERS, which removed all my apps and wouldn't find anything, so I had lost Apple TV, Disney+, etc. Not sure whether it would be possible to get it back to US/US now, without a VPN, but that's not really a concern, as I have no intention of moving back to the US.