If you have a Generation4 TV-B-Gone you can modify it by adding a switch to choose between European POWER code transmission or US POWER code transmission. First check if your TV-B-Gone board looks like the one pictured below to see if you have a Gen4.
Note: If you have an older version, you might find the answer in this
instructable of the inventor Mitch Altman who had helped me a lot, modifying the new version.
You need a very small switch (some sort of smt switch) to fit in the original case. If you got one, figure out where to put it - best would be the side of the board where no other parts than the battery clip is mounted. Check the other half of the case - there is not much space and find a good position.