I have found an answer which is to remove it and add it again. That doesn’t seem to work. I have gotten an update by clicking on the recycle button in JavaScript. But only the first time and second time with some struggle. Is there a foolproof way to make a change to an extension then reload it for testing?
I am wondering about clearing some kind of cache?
Something nice that could be added would be to be able to edit the extension in MakeCode itself. Given the lock icons it looks like that is not allowed.