All of our beacons come by default with txpower set at max. If you reconfigure one of our beacons with Gimbal Beacon Manager, it will require that you create a new configuration in the Gimbal Manager portal for the settings, including the transmission power settings, you'd like.
While you can't than query the beacon directly for txpower, you can query the configuration if that's helpful via REST API. Documentation on the call is available here but visiting Get A Beacon Configuration
Reducing txpower from its maximum has a negligible impact on battery life in our tests and is rarely required given the way our zero-configuration beacons are designed to work. We recommend always keeping them at full power.