Latest firmware transmits at 2 Hz in URL mode, 1 Hz in RAW mode.
April firmware transmits at 2 Hz in both modes.
Right now easiest way to configure transmission power and is to change the setting in configuration and recompile. [EDIT] Same for intervals.
Currently both accelerometer and BME280 can be configured over GATT, however there is not exact date on when the transmission power and interval is configurable. Probably sometime during 2017.