If I was informed an a/c had just changed to non-RVSM and was heading south toward France, I would instantly drop said a/c to FL290, get the standard 'NON' from Monsieur Brest, and then continue the a/c down FL270 and hand-off that way. What happens next can vary, 50% then get climbed back up to FL290+, normally those with French registations or ties. Similar things can be seen heading Maastricht way if the German watch is on, but the climb back up NEVER happens
