Tickets without change fees are getting rare those days, even in F class.
Rare or very expensive. CX often has reasonable change fees. But the real expense can be fare adjustment when your fare bucket is not available anymore on all or part of the itin.
So check what kind of change fee you can get, rather than looking only for zero.

Since I stopped getting other people to pay for my tickets (:D), I have always travelled PE to Europe, E tarif I think, and I know that have changed a couple of times without any fees, or even any fare adjustment. Whenever I was looking at changing, it actually seemed that the PE fares don't vary that much, but maybe I was just lucky.

Your advice is good, especially since I hadn't focused on the difference between a connection and a stopover - despite years of travelling, I have never needed to know the difference, so at least I am now alerted to what to look our for !

BTW, I do not share your enthusiasm for AF website. Indeed their mobile app is now good. But AF usually only provides you with the cheapest and possibly fully flexible fares. Not possible to see what are other fares with different restrictions as some airlines do. CX website is no better.

I only use AF now for simple CDG - EDI - CDG flights and I actually find that the app always gives me what I need in terms of options price-wise, but that means I can't really judge well, I suppose.

My comments about the websites and apps were related to user friendliness and general layout, where I really like what AF does, compared to the heap of garbage that CX has put out there !