It would be nice to be able to add metadata to the run_x_to_nwb_conversion.py command. In nwb-conversion-tools, we handle this with a YAML file that turns into a hierarchical dict. For instance, you could supply a YAML file of the form:

NWBFile:
  session_id: '00003'
  session_description: 'Description of session'
Subject:
  subject_id: '0001'
  age: 'P30D'

run_x_to_nwb_conversion.py would turn that YAML file into a dict and and then ABFConverter and DATConverter would take that dict and populate the NWB file accordingly.

This relates to #364 as well. pynwb acts more straightforwardly if you can write all of the metadata in the initial write. It would be better to specify the subject ID during the creation of the file rather than write it in after-the-fact.