This is similar to the situation where you buy a car that can reach speeds of up to 280 km/h, while the city speed limit is 60 km/h and the highway speed limit is 120 km/h. Therefore, you are concerned that the vehicle registration office will not issue you a license plate.
Using a 1000W machine to register is also fine.
Transmitting more than 15W is considered an illegal operation, and your maximum allowance is 15W. What are the specific penalties? You can refer to relevant cases for details.