Yeah, considering EYG's observation of the Italian situation, it's probably not worth worrying about the Pope's edicts, and simply bum-rush the Italians down to Tuscany. Playing tippy-toe with excommunication may just stagnate the Empire, getting you nowhere. The influence gained from blitzkrieg conquest can serve to counteract the big knock you take from excommunication. If you choose this option, though, I would suggest attacking the Italians and ONLY the Italians, and to actually accept offers of alliance from other factions.

I guess what I'm saying, in a rambling kind of way, is any conflict with the Italians should be all-or-nothing.

Of course, this all goes out the window in those weird campaigns where they have that "special" relationship with the Pope, and he calls for crusades against you within 3 or 4 years of your first assault against Italy. Kiss your empire goodbye if anyone buys a ticket to THAT show.