add genre to existing multi genre tags

Hi Guys,

I want to add new genres to (different) existing (multi) genre tags.
For Example:
I have files currently tagged as "disco; 80" and "New Wave; 80" and so on, and now I want to add a new genre (batch) to these tags. In the above example, the outcome would have to be: "disco; 80; Instrumental" - "New Wave; 80; Instrumental"

I tried to leave the genre fields set to "keep" and then added the new genre with a ; separator, but that doesn't work...

How do I solve this?

Is this string "disco; 80", that what you see in Mp3tag "Extended Tag View" to be the content of the GENRE tagfield?

If so, then you can do it like it is described there ...

If not, then come back and tell us more about the content of the GENRE tag field/s, you might see in Mp3tag "Extended Tag View".