Hmmmm...that's a tough call, but i agree with Roger that if the fixed cup is in good shape, leave well-enough alone. It would sure eat at me, though, if it were mine. If the cup is bad, or gets bad enough, or you just can't stand having it tacked in place...you can always remove it and if the threads are bunged up (beyond repair) have the BB shell reamed and retapped for Italian. If so, I'd opt for a Phil BB with Italian rings and that'll last "forever".