Following discussions on DM-18170 and with Robert Lupton, I am going to add infrastructure support to astro_metadata_translator to allow files to be written that will contain updates to headers.
I am proposing:
1. Pre-examine the header, determine the instrument and obsid.
2. Look for a file of name relating to the OBSID (yaml or maybe JSON containing override values for specific headers).
3. Apply the corrections from that file to the header.
There will be a standalone function for automatically updating a header, and support inside the ObservationInfo constructor to apply the correction automatically. The location of the correction files is an interesting discussion but will probably be per-translator specific but allow overrides using a PATH-like environment variable.