However, it would be nice to add InspireHEP as one of the resources to fetch bibliographic data from, so these keys can also be fetched from InspireHEP for entries, which had been imported from elsewhere or are missing an citation key.
The usual procedure would apply, i.e. the opening of a window, which shows the differences between the old and new entry and letting the user choose how to merge them etc.
this depends a bit on the fetcher, but I think this could be implemented. It would only be useful if you could maybe help to identify which fields of the entry should be used for a query. Search tips for using INSPIRE – INSPIRE help