hello!
...does someone the reason i cannot change the "dataquality" field writing
a mseed file with obspy?
from the souce code of
obspy/mseed/__init__.py
Hallo.
This problem was fixed in changeset 1841: http://www.obspy.org/changeset/1841/obspy
You might have to update your obspy.mseed module.
To use it just set trace.stats.mseed.dataquality to any value currently supported by the SEED format (D, R, Q and M).
Best wishes!