You can copy tags in MC. Should be in the wiki.
Select files.
Copy the tag (ctrl-c)
Paste the tag (ctrl-shift-v)
Try a few before you do very many.
Thanks for you reply but this doesn't work. I'll try to explain myself.
1. The date field is empty when I imported the flacs containing no "DATE=" tags but only "YEAR=yyyy-mm-dd"
2. once I entered a date manually MC is removing those YEAR tags, and added "DATE=yyyy" (without "-mm-dd")
It did add a JR-DATE tag which is useful for MC, but other programs don't know that, and so the full date is lost for those.
I retried this when I manually replaced the "YEAR=yyyy-mm-dd" tag by "DATE=yyyy-mm-dd",
and then MC was able to read the DATE tags correctly.
But the real issue then is once I change an incorrect date, fi. 2010-5-20 to 1991-5-20, then
MC would save "DATE=yyyy". (so the "-mm-dd" part is gone!)
I know JRiver also adds a JR_DATE but that is usable for MC only but my other programs can no longer see the month and day.
Wouldn't it be more logical is MC saved "YEAR=yyyy" and "DATE=yyyy-mm-dd" and not "DATE=yyyy" ?
I'm willing to change all my flacs to contain DATE=yyyy-mm-dd i.s.o. YEAR=yyyy-mm-dd so MC can read those,
but I would like that MC is not removing the -mm-dd when changing dates from within MC.