No, it won't. But it's almost guaranteed to be unstable (if not immediately, in the near future).
But it is highly recommended to flash the new firmware, do a full reset to factory defaults, and then do a minimal and manual router configuration.
Be sure you read the changelog file(s) and modify your use cases appropriately.
Use the correct method to reset your router from the link below (after you've flashed the firmware you want to use).
Das ASUS Support Center hilft Ihnen Treiber, Handbücher und Firmware-Versionen herunter zu laden. Hier finden Sie auch FAQs und Troubleshooting Hilfen
www.asus.com
The following link(s) may also help get the best performance out of your router.
I have an ASUS AX86U and contemplating the installation of Merlin firmware. The DDNS settings on the AX86U are limited to select dns providers. If I install Merlin, will I have more flexability (choices) with the DDNS Settings? Thanks in advance!
www.snbforums.com