Some additional communication in app would be helpful when features are unavailable (such as the greyed out subdomain field). A message that says something to the effect of "The ability to X [ change the default subdomain] is not available yet. Please add an additional domain to your workspace as a workaround... etc."

That would cut down on help tickets and frustration from wasted time thinking there was a setting somewhere.

In fact you could do this for all of your common requests and cut down the workload for your tier 1 agents. Once a feature is implemented, you could simply remove the tooltip (and have that in your default implementation workflow so it's not missed when resolved).