Just thought I'd throw this out there, so that you can say "yes I can" if an agent ever tells you that you can't....

This morning I was to fly JFK-MIA-SJU. I missed the JFK-MIA segment because the JFK AirTrain was broken, and only running in one direction. I tried to get on the direct SJU flight but it was oversold. I convinced the gate agent on the SXM flight to let me go JFK-SXM-SJU, which she warned me might get me stuck in St. Marteen (how tragic). Anyway I cleared both legs, with the upgrade, and got to add a new stamp to my passport. ^