Just use Migrate or any app you like for app backup. It doesn't take more than half an hour.I wonder if this means that everyone on the 25 Dec official build will need to clean flash if they want to go onto any newer upcoming build of Arrow, official or otherwise.
That would be really annoying as Dec 25 build was the first one I came to for A12 and obviously had to do a clean flash to get onto that from A11 so another clean flash so soon will be frustrating.
What are you doing flashing "early/beta" roms if you're going to complain about it? Stay miui-stock if you don't want to bother.