Answering here since I struggled with this too. I tried to run the firmware updater for DWM-222 rev A2 firmware 2.0.1 in Windows while already being at 2.0.2 and the update script would not recognize the device and eventually time out/quit. I assume this happens because the device gets new USB product IDs once it gets updated to 2.0.2.
So I run the updater again, and while the updater was trying to find the device, I unplugged and replugged the dongle, and it seems that for a short while the device reports as an ID recognized by the 2.0.1 update script and this triggered the update to continue.
IIRC it then proceeded to flash the different partitions of the memory, and at the very end it got stuck (once flashing the "CD" image I think) but it was late enough that the important part had already been downgraded. I took the risk and unplugged the dongle then and it was working on 2.0.1 (including QMI, but I just tested with standard Linux and not OpenWrt). I imagine that trying to reflash 2.0.1 if you're already 2.0.1 should complete without issues, but I didn't take the risk since it was working for me.