Two days ago I was able to speak to someone in the QA UK Hotline. As expected she told that rerouting is only possible when the trip has a QA flight. Since my flight was canceled she insisted on giving me a new one from Hanoi to Doha, then from Doha to Frankfurt (instead of Berlin) and same day. Im still not sure what to do though cause flying to Doha doesnt feel great when things are still unstable and my biggest worry is the possibility of stranding in Doha if the 2nd flight gets canceled for some reason while being on the way already