Map-ac2200 upgrade and return to factory default

I am keen to use OpenWrt on my Asus Lyra map-ac2200 but before doing so,
a) I would like to ensure I can return to stock firmware at a future date. Can this be done? If so, how and does it work?
b) the instructions for installing OpenWrt map-ac2200 require running the sysupgrade command, however this command does not appear to be part of the firmware. Is this command deployed in the .itb write or is it already in the stock firmware. In the case of stock firmware, what version of stock firmware do I need as it is not in my current running stock firmware?

These questions are similar to existing topics: Revert to stock firmware on Asus MAP-AC2200 and HELP: Asus Lyra MAP-AC2200 Mesh install issue

For this device, it's a two-step process, you first flash the OpenWrt initramfs image using the OEM firmware's mtd-write, once you've rebooted into this OpenWrt initramfs image, sysupgrade will be available and needs to be used for step two.

Anyone know if it possible to revert to stock firmware after installing WRT?