Just had a look. Looks good! A few comments:
1. The tests are internal, using simulated events - it's worth testing
the integration (I mean defining a few dummy classes and changing them)
because it is very easy for the integration work to be broken when
someone patches the compiler with something out of date.
2. The "System" in the names isn't very intention revealing - I wouldn't
guess it is about code specifically. Maybe Code*Event,
CodeChangeNotifier?
3. The tests are a bit too indirect as examples - they don't show how
easy to use the framework is!

I simply did -

a _ SystemChangesDemo new startDemo.
Where -

SystemChangesDemo>>startDemo
	SystemChangeNotifier uniqueInstance notify: self ofEvents:
{#renamedEvent:}
		using: #event:.

SystemChangesDemo>>event: anEvent
	Transcript show: anEvent.
	anEvent explore

and then renamed some classes.

That's it. I would very much like to see this get into 3.7.

Daniel
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