Hi Les,
First of all please accept my apologies for the delayed reply, but I had to double check on this answer with my dev team.
Unfortunately current we do not support to add "Connect As" & "Authorization rules" at the Site & Web Application level under "Custom Properties" section from "IIS" page. However, we do have an improvement to expand our custom properties support in the future and I noted down your request on this too. As soon as it will be available we will update this forum thread.
Also, in regards to your second request, I'm afraid we do not have built-in support for Authorization Rules removal. To achieve this you could try to develop your own custom action.
For now the only way to implement both of your requests if through a
custom action.
All the best,
Daniel