I don’t run captive portal so I’ll give it one more shot then maybe someone else who has done this can jump in.
If you copy your version of cp_showauth to /Database.
In the web interface Setup -> Startup/Cron
Add the following to the post boot script:
rm -f /root/kerbynet.cgi/template/cp_showauth
cp /Database/cp_showauth /root/kerbynet.cgi/template/cp_showauth
make sure the “Enabled” check is set and save it. (check your permissions on the file so they match)
As long as you have a profile saved and activated it the file should persist and the startup script should replace the built-in with your copy.
Hope this helps – if not let me know if you answer it – be nice to know if I enable this in the future.