Can we install product above FCC test power level declared in certification report
When you have an approval and need to change something, you must be able to reason about if the changes will affect radio and/or EMC characteristics. In this case it's crystal clear: you have to repeat the test. Changing output power to something 5 times larger than tested is a very drastic change. There is no doubt that it will effect most of the radio characteristics, including out-of-band/spurious emissions.