Equivalent of french CAPES or agrégation exam without having to teach
Note that if you pass the &quot;agrégation&quot; (i.e. successfully pass the exams) but don't teach after, then you cannot call yourself &quot;agrégé de mathématiques&quot; (as it's reserved for people who then teach) but you are allowed to say on your CV that you successfully passed the exams (I think it's &quot;reçu au concours de l'agrégation&quot;, but not 100% certain). I shall not comment on the morality of potentially taking up a place in a competitive exam with limited number of places (the Mathematics one always has more places that admissible candidates, but still...). However it sounds like a lot of effort just to get a diploma.
The more traditional route is to get a &quot;Licence&quot; in another subject by taking online classes -- so there aren't any mandatory classes -- for the year of L3 at a nearby University (provided you can get an equivalency for the first two years of L1-L2), and taking the exam. It's not uncommon for students in Physics, Mathematics, or Computer Science for instance to get one or more degrees in related topics this way. If the secondary discipline is less closely related to Mathematics (say Philosophy or Ancient Languages), then it may be trickier to get the equivalency, although it's always easier to go from Mathematics to anything else than the reverse.