Unfortunately, nothing happens when doing so. I only get a busybox instance that does not give any logs or other outputs when I try to install OpenWRT from the web UI.
Are there other options to obtain error logs?
Edit: Wouldn't it suffice to bump the soft_ver to something like 1.1.8 for the update to be accepted? I have no experience in building OpenWRT firmware with patched firmware-utils. If someone would give me directions, I would be happy to try it instead of soldering...
Edit 2: After some research, I found a hacky solution, that lets me install OpenWRT without soldering. This worked by using the same trick @mrm used on the TP-Link EAP225 [here]. You basically directly edit the OpenWRT Factory Binary with a hex editor. I changed the string
00 00 00 10 00 00 00 FF 00 00 00 20 23 10 09 00 00 5B C9 00 00 00 01
to
00 00 00 10 00 00 00 FF 01 01 09 20 23 10 09 00 00 5B C9 00 00 00 02.
That changes the alleged version of the image to 1.1.9 and bumps the compat version to 2. The TP-Link installed the update and is now running OpenWRT! 