The A/B system can probably be altered by editing Boot Image files. Well, You can now Install Mi A1 Android One Firmware to the Mi 5X, Thanks to developer "heli0us". Additionally, all aspects of the phone are working as expected (No bugs).
You'll need to Unlock Bootloader and Install TWRP Custom Recovery in-order to Install the Android One Firmware on Mi 5X Tiffany. You can grab the Custom Rom ZIP file from below.
The Firmware is based on Google's latest Android 7.1 Nougat. However, Google plans to roll Android 8.0 Oreo update to Mi A1 by end of 2017, this also means that the Mi 5X will also get Android 8.0 Oreo via Port.