[digital_carver]

It seems like every metadata provider has their own identifier number (asin, google, goodreads, etc.), and they send that in along with the other pieces of metadata. Currently, Calibre doesn't allow not downloading this piece of metadata (apparently for some internal technical reason?), which means that in many cases the existing metadata is overwritten by some custom piece of identifier.

For example, I'm right now in the middle of going through my bulk metadata download results, and in 90% of the cases that require change, the change is that the local "mobi-asin" is about to be overwritten by "google" or "goodreads" identifiers. I wish to use the tags and such metadata from these providers, so disabling them entirely is not a solution. So in every case I tab to the existing identifier field, Ctrl-c, shift-tab twice to get back to downloaded identifier, and paste it there (I wish to merge, not overwrite, so the arrow button doesn't help.)

If it's not possible to disable the identifier metadata download, could an option be added to merge the existing identifier with the new ones, if the new ones don't contain an instance of the same identifier? (ie., merge existing local "mobi-asin:yyy" if downloaded data is "goodreads:xxx", but overwrite local "mobi-asin:yyy" if downloaded data is "goodreads:xxx,mobi-asin:zzz").

Is something like this already possible through some preference or plugin? If not, please consider adding it as an option.