I think this is solved as I wrote in the forum thread.

Learned something new: When I tried to revert the wireless.js in luci to a version offering the configuration for #ppsk aka #dpsk I controlled the downloaded version in the debugging window of #firefox.

Right there its possible to download a javascript file from the debugger to a file, change it and use it inside the opened web page. No need to change anything on the server serving the original js.

It seems I'm stuck on the #OpenWRT side. Don't know how to configure #dpsk (dynamic pre-shared key).

https://forum.openwrt.org/t/dynamic-pre-shared-key-dpsk-via-radius/193298?u=chrichri