If you start putting through edits, other editors can vote and comment, so the conversation is usually held in the edit notes. People who've subscribed to the artist will be notified of your edits, so they'll be aware of what you're trying to do.
To my knowledge, yes, it's going to take a lot of edits... Starting with each release you have to change the artist to the new artist, make sure it's changed for every track, and the release group, and the recordings, and then do that for each album... It's much easier to merge than to split artists unfortunately :S
Maybe someone else has a quicker way to do it that I'm not aware of!
One thing though, I'm not convinced that they should be split!
You haven't provided that much evidence of it being a seperate project. It seems like he interchangeably used the different names and his musical style hasn't varied that much (or at all?) between the two. According to Wikipedia he 'retired the onelinedrawing moniker in 2004 and now intends to put all future solo releases under his name'. Since he's 'swapping out' the names, it doesn't seem like they're distinct from each other. If he was performing under both names at once, and each sounded very different, that would seem more like different artists to me.
Last.fm unfortunately is a very bad example, they simply lack the functionality to deal with artist name variations.
MB does have this functionality, so when you tag using the current un-split artist, you will still get the correct relevant alias tagged into each release (so it will be scrobbled under the appropriate name for each track, for instance). So on a practical/ tagging level you shouldn't have to worry too much