If you do a search on this forum you'll find all sorts of advice both practical and superstitious. Basically, if it's part one registered you have to check with the MCA if the name you want to use is available, then do the paperwork. If it's SSR you can call it what you like, but still have to do the paperwork. If it's not registered at all, you just change the name - then do the superstitions bit.
Having had 3 boats named "Miss Noma 2", "Manglewurzel II" and "Ronlinda" I felt obliged to change the names of all in the interests of good taste! I am currently touching wood as I write this but have suffered no ill effects to date. I never walk under latters if there is a less dangerous alternative route.