Change default port
It would be nice to be able to change the default port for the WebUI
You already can, just add the switch.
--webservice-port=8200
Then change 8200 to whatever port value you want it to be at.
See https://duplicati.readthedocs.io/en/latest/07-other-command-line-utilities/
Does this also work for auto starting Duplicati on MacOS?
This is more of a question for the Duplicati forums than it is an issue with Duplicati, but to answer your question, yes it does. In /Library/LaunchDaemons you'll have a file named something.Duplicati.something, open it in a text editor and make the change.
The requested capability sounds like it's there already. Can this issue be closed?