You can't modify OBS settings while any OBS output (encoding) is active. You can try to make and run the script as mentioned in:
I can not figure out what video output is still running thats perventing me from editing my video settings. Any help?https://obsproject.com/logs/40mfFX8faB2uu6Ke
obsproject.com
this will help to you to find out what output of OBS is still active (by looking into the log-file of OBS after using the script, later you can remove the script).