How to change the bits per value in a GRIB message?
Step-by-step guide
This can be done by using the grib_set command.
You can use the "setBitsPerValue" key as in:
% grib_set -s setBitsPerValue=17 in.grib out.grib
or use the "repack" option:
% grib_set -r -s bitsPerValue=17 in.grib out.grib