Used this trick to change the seat and… it resulted in the disaster. During the boarding, all was fine. Once on board, ground staff paged me and wanted to see my boarding pass. I showed it and they communicated to the team that indeed I boarded (even if there were no issues during the actual boarding). Upon arriving to LIS, the luggage didn’t make it, as they had offloaded it in FAO. Apparently, altering seat cancels your original check in. Despite boarding with the new boarding pass, the system offloaded me and the luggage. TAP being what it is, it failed to load the luggage on four consecutive flights between FAO and LIS that took off on the same day. Now it says that it should arrive today, but I will believe it when I see it.
Apparently, TAP wishes me to do shopping at their expense.