I got the same advise in the norwegian forum for geocachers as people here has given - just created a new account, and copied the loggs adding a line about the name-change. Worked fine, and havent got any negative feedback yet for the new loggs. (Deleted the old loggs after logging under the new username).
One thing I havent figured out yet; I bought two TB's before I changed my username. Of course I activated one of them, to see how it was done.... Know I wonder - are there any way I can adopt it over to the new name? I've got the activation-code and everything, the TB has not travelled at all, just activated it. Would be a shame to just throw it away right after purchase... Any tips?