Update only changed - possible?

General Discussion
#1

Hello!

Say I have some files in mp3tag file panel. A few have cd cover embedded. I select all files, then cover art deletion in left panel, and click Save icon.
Now, is this possible to have tags changed only in files from where coverart is deleted? It seems tags are written to all files.

TIA

#2

add a column that displays the field %_covers%
sort by this field so that the ones with and the ones without are grouped.
then select only those without cover and update their cover.
It is not possible to write only an update. Any writing is absolute.