How to patch:
1. Buy Kaitou Rousseau (Really, it's a great game and they deserve your money)
2. Obtain a ROM image, (Not trimmed!!), of Kaitou Rousseau (No I won't tell you where, don't ask)
3. Unpack your Kaitou Rousseau ROM, I used DSBuff, use whichever tool you prefer.
4. Copy the data...