It's a BIG deal! Always follow the local ceremonies/beliefs.

I hear it's bad luck if you change the name...

BUT if you change the name you have to put the old name somewhere on the boat....I did this when renaming the Chris Cat I bought...superstition?..maybe?

I renamed mine, and had a trouble free, awesome first summer of boating - I am sure I have jinxed it now, but I wouldn't live with a name I don't like.

That tale goes back to the Clipper Ship days, about 200 years ago...

I KNOW it's bad luck not to Christen a boat before you take it on the water! :

I was told that if you change the name you need to keep the old name on the boat somewhere else. We always put it under the dash.

http://www.boatsafe.com/nauticalknowhow/rename.htm

I bought my boat with GET DOWN on her I feel the same way I just don't want to ad anymore problems then I have to so I added a few.. Now its GET DOWN WITH THE SICKNESS.

One tradition i heard of was - before you re-christen, you write the old name on a piece of paper, jamb it in a bottle full of water (so it will sink) - cap it and throw it in a lake. I imagine the Litter Police frown on that one.
Another option is to rubber-band it around a rock. More biodegradable, I guess...

It's only supposed to be bad luck if you change the name if you already own the boat and have named it. Buying a new or used boat and changing the name is 100% acceptable to the supersticious gods. That's what the old maritime law says.