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.
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Step 1: Modify the Case
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.
Step 2: Glue the Switch and Solder the Parts
If you have an european version, desolder R3 first. The left pad is connected to ground, the right side to pin 5 of the microprocessor (thanks to Mitch again for the schematics). The US-version shouldn't have R3.
Glue the switch in its position.
Solder a small cable from the right pad of R3 to the switch.
Solder a 1K (or something like this) resistor from the other pin of the switch to ground (I used the middle pin of the resonator).
Update: Mitch was nice enough to let me add the schematics for you.
Step 3: Test It
If you put the batteries back in, the red led of the TV-B-Gone will blink 3 times if the switch is open (US-mode) and 6 times if the switch is closed (EU-mode). If you want to test it and take out the batteries, you have to wait a minute or so, to let the condensator discharge (otherwise the microprocessor won't reset, and the led won't blink).
Step 4: Case Closed
From now on you have a few more chances to turn these TVs off. I've found 2 LCDs near my place, that need to get the US-codes.
Little fun fact I've noticed: One of the last codes sent (in both modes) is the code to send any Apple Mac with an IR-Receiver in sleep mode, if it isn't paired to a single remote (that's standard).