If you set 0x493 to zero the game will think the status bar has zero scanlines, and so simply won't make it appear. It's a neat little trick if you need the status bar temporarily gone, and need the hack quick. Now, the problem with this is if Mario should hit, say, a message block, Layer 3 is altered, and suddenly everything shows up.
I've hacked it so that I can choose whether or not a status bar shows up at the start of the level, but the whole poofing out of nowhere bit is pretty annoying. There's got to be a better way then pretending there's no scanlines to write, but I don't really know enough about the rest of the process to disable the status bar any other way.
Here's that hack I made, just in case anyone's interested. I cut out some stuff I didn't think was necessary for the post and haven't tested it since, but it should still work.
; Disappearing status bar hack