I posted the question so I could answer it.
The official response is that there's no way to do it. The expert responses here say there is no way to do it.
There is a way to do it easily. It took me quite a while to find it even though it is incredibly simple and should have been something I and anyone else come up with right away. Instead of posting the answer right now I'm going to come back and check what people come up with. My one request is this: if you believe it isn't possible or very easy to do, please know that it actually is. Nothing extreme, something extremely obvious, but I have the sense that Apple users - I have been one for quite a while - tend to want simplicity and don't, as a group, want to think about how to solve things like this. They'd rather look for the official answer and that keeps getting repeated. I've been stuck with it as a problem for years, and suddenly yesterday I found two solutions, one too destructive of other things and the second completely perfect, easy, and it changes nothing other than exactly what I wanted to change. It will tell you exactly which ones are set, you can then remove them individually or you could probably change them all at once, I haven't tried that because it isn't necessary. Once I knew which they were, I could change the ten or twelve out of over 2,000. It can be done within minutes without any third-party tools. Probably, actually, I could now do it within less than a minute if I had to.
Sorry if this seems annoying, but after two years of "experts" telling me it isn't possible and leaving it at that, I'd like to know if any Apple users have a mind for this kind of thing. I know a lot of intelligent people use Apple products, but I just don't think we tend to think of using that intelligence to think even slightly outside the box. This is barely outside the box at all. So simple.
