is there a way to set a location as not discovered?

There's no console command that I could find on the wiki.

Doing a google search gave me this forum link, where somebody is trying to do something vaguely similar, and the closest thing to a usable response was to try and edit the save game file, which I don't know how to do, and I'm assuming you don't either considering you're asking this question, so I think you're out of luck trying to do the specific thing you want.

However, to answer your deeper question

You might want to look into the console command "PlaceLocationMarker". I've never used this, and you want to save your game before using it, but supposedly it lets you add new locations markers, and choose the colour? So theoretically, instead of marking a location not discovered, you could put your own location marker there, in a different colour, with the name "look at this again later", assuming that's how it works, and they stay on your map after you save and reload, and you can figure out how to get it working, etc.

Also, again unfortunately, even if that does work, there doesn't seem to be a good way to remove a specific marker, only a command called "ClearLocationMarkers" so you might end up with a bunch of markers saying "look at this again later" when you have, in fact, already looked at it again later.