Is there a way to revert an android version update without flashing a ROM? I'm not very familiar with the Android system, but I recently updated my phone from 5.0.1 to 5.1. Unfortunately, one of the games I play doesn't support 5.1 yet, so I would like to revert to 5.0.1. From what I've read online, the main way to do this seems to be to flash a ROM on your phone, which, as I understand, is similar to factory resetting your phone with an older factory image. The problem with this is that it seems it would also delete the game data.

Is there any way to revert back to version 5.0.1 without this process?
There's no sort of "rollback" feature on Android. Due to device space limitations the old OS image is not kept around.

So to downgrade you'd have to flash. It's not necessarily the case that you'll lose your data when doing this, but it depends what the ROM's updater script does and whether the ROM will work with the data left by the previous version (you might need to manually factory reset, which is generally recommended before flashing). As Andrew noted in the comments, unlocking your bootloader will wipe the device so if you need to do that to flash then you're out of luck. As such it is always recommended that you do a backup before flashing.