The CAM-M8 hasn’t got anywhere to store the custom config. You would need to set it every time you boot your Pi and you know there is no power in the superCap.
e.g. change to 2Hz(twice a second)
echo -e -n "\B5\x62\x06\x08\x06\x00\xF4\x01\x01\x00\x01\x00\x0B\x77" > /dev/serial0
Regarding the IMU, Which code are you using and is it unmodified (except for calibration values)?
Peter --OzzMaker.com --