I would like to make a "disable minimap" type of skill, which when used will make an area of the minimap black (such that you can't see enemies or allies on the map). How can I accomplish this?
While I'm far from an expert on SC2 modding (having barely even played the game), I've stumbled across this question in the archives here several times and each time I've gone out researching ways in which this might be accomplished.
Unfortunately, every time I've come up empty, and I have to conclude at this point that it's not really possible to use the SC2 mod tools to blacken or "re-fog" a portion of the game.
I did some across this thread, however, which is about solving a problem of 'radar tower' like units, and which you may be able to modify to achieve something similar to what you want:
Make a unit with an event, when other units come within a certain radius of that unit, apply a visibility modifier to hide that unit. You'd need to do some further scripting to render the primary unit non-player-controllable, probably, and it won't replace the fog of war on the map, but it could result in making anything that walks into that range invisible, which may be close enough for your purposes.