Well, going strictly by the "heads up" bulletin thing you should be OK. I would imagine it will come in less than 45 MB since they have told people to have 45 free (you always build in a little padding).

I don't think you'd free up much just by disabling a repository...I can't imagine the little db files taking up that much space. However, as I said before I don't think you're in trouble space-wise so long as you don't make it worse than it currently is

I wonder if there might be a simpler solution to all of this though. If the space is really just needed in order to download/unpack the files in preparation for installation...couldn't they just be downloaded into /opt by the update software? It's not like this is a performance-critical kind of thing we're dealing with. Just a random /ponder on my part.