Thanks for coming back to me, evmatter! Wario Land 2 was my childhood, so your editor made me really excited about this, hehe.
I have been using your editor to edit most of wario's sprite so that they slightly resemble the sprites of Wario Land 3.
I've basically been cleaning all the tiny pixel errors that the developers left in Wario's (and some bosses and enemies) sprites.
I've posted a first version of it here: http://www.romhacking.net/hacks/2990/
So, the finishing touch that I just needed was to edit Wario's sprite in the ending credits, and there was some feedback that I got from friends that I have yet to implement.
But after that, I could say that it's finished!
Oh, and what I DID manage to edit using a tile editor, was Wario's celebration sprite that you see only once when you've completed the game for the first time. It would be cool if that was in the editor as well, but it's not that mandatory, since I was able to figure that out myself.