Can I change the output power of a BT800/BT820?

Answer

Yes. First, you'll need to have access to the pskeys. On Windows, you will need to obtain the Bluesuite from CSR. After opening Pstools, you can search the pskey "PSKEY_LC_MAX_TX_POWER" and modify the maximum TX power. As the module contains an eeprom, it will store the setting, and you will only need to do it once.