What if you made all of your extra-Schengen travel via connecting airports outside of Italy? That is, perhaps you connect through CDG or MAD every time you travel outside of Europe. Since all of your entries and exits from the Schengen region would be outside of Italy, would they have a chance to enforce the passport tax stamp?

That'd probably work, except perhaps if you're an Italian trying to claim a VAT refund on exit. The French, for example, aren't responsible for collecting Italian passport taxes and don't check for the stamp. Crossing the Italian border via road or rail works since there's no passport check at the border.

But it's a little strange that the most expensive passport to use for ex-Schengen travel to/from Italy is probably the Italian passport.

Had mine ammended
 

I needed to have pages added to my passport back in 2007. I had it done at the Consulate in Munich. I was studying near Ingolstadt at the time. I mailed it into the consulate in Munich in a envelope with a prepaid, registered envelope. Got the passport back in the mail after about 8 days from the consulate. IT was added in this fashion.

Clear tape, and stitched. Also there is an official sticker/seal type thing stating the date the passport was ammended and where it was ammended (Munich, Fed. Rep. of Germany)

I was hassled by Customs Officials at Cancun Airport in December of 2009, because the Agent claimed to never seen something like this before and took my passport.. literally under a microsope and scrutinized it thinking the passport was a fake or something.