That was on my mind when I wrote that — it's not possible to merge data, and there's no point in not using the device while traveling and avoiding taking photos

That was on my mind when I wrote that — it's not possible to merge data, and there's no point in not using the device while traveling and avoiding taking photos or sending messages (that aren't saved on some cloud platforms). One alternate solution, if you feel safer after the border crossing event, could be to use the native cloud backup feature of the phone maker. Backup the phone on the cloud, wipe it, set it up with a new email address, and then once you cross the border safely, restore from the cloud and start using it. You wouldn't have to worry about merging data then. But the issue here, at least for me, is that I don't want to backup my data on the phone maker's cloud.