If I'm taking the PSM I exam...
My answer is to continue to have retrospectives, but it's been a while since I took that exam and I don't know first hand what the "correct" answer is.
Also, I have always interpreted the "self organizing" aspect of the team to be "self organizing to do the work", not "self organizing to change Scrum."
In short, it is not the role of the Dev Team or PO to change Scrum. It *is* the role of the SM to enforce the Scrum principles, roles, etc, and make sure Scrum is followed.
These sentences in the Scrum Guide seem relevant:
"The Scrum Master is responsible for ensuring Scrum is understood and enacted. Scrum Masters do this by ensuring that the Scrum Team adheres to Scrum theory, practices, and rules. The Scrum Master is a servant-leader for the Scrum Team."
I've always interpreted this is as: "The Scrum Master makes *sure* that Scrum is followed, in the nicest way possible."
If the team rebels against this, I would look for some underlying dysfunction or team level impediment and try to get it solved. If that doesn't work, I'd escalate to someone higher up, in the nicest way possible. :-)
I have always viewed the "inspect and adapt" motto to mean "inspect and adapt, *within* the Scrum framework."