This was the subject of a very long-running (and award winning I think) thread on ybw.com a few years ago.
There seem to be many tales and legends about re-naming, mostly based around the myth of bad luck, and just as many on the subject of how to mitigate that bad luck. For every tale of eradicating the name from the vessel, there's one of retaining the name somewhere permanent. Heresay and speculation are rife.
One thing seems to be agreed however.... the renaming ceremony should be an auspicious event and merriment should be the order of the occasion; the champagne, cava, rum and any drink should flow freely! Under no circumstances should the boat disappear one day to re-appear quietly under a new identity, and woe betide the owner who sanctions such a move!
But of course there's even exceptions to this rule