Tagging Question, Tag - Tag without disturbing what's already there

What I'm trying to do is, take something from artist field and put it in album artist field, without disturbing what's currently there, for example.

Artist: Nirvana
Album Artist: Various Artists
INTO
Artist: Nirvana
Album Artist: Various Artists; Nirvana

how do I do this in Convert : Tag - Tag because I want to do a batch of these.

If you use Convert>tag-Tag for ALBUMARTIST, try
Format string: %albumartist%; %artist%

I am not sure if the whole affair in itself makes sense.
Most players use ALBUMARTIST as grouping criterion to keep an album toghether - so ALBUMARTIST should contain the same data for the whole ALBUM.
The data in ARTIST can vary without ripping apart the ALBUM.
Esp. with "Various Artists" and the appended data from ARTIST you will create a lot of different ALBUMARTISTs for the same ALBUM and your player may now display an indvidual ALBUM for each.

This is true... It didn't work, the real problem I'm having is, if I click Nirvana in Musicbee, I see all their albums, but there are hidden songs on soundtracks and compilations, that I don't see. because it's grouping it as Album Artist and the Album Artist is Various Artists. I thought I found a work around. should of known. well maybe I'll find some other way.

I'm just using Nirvana as example, this is ofc happening to hundreds of artists I have in collection.

What didn't work? The format string that I suggested did not append the data in ALBUMARTIST?
Or the appended data did not lead to the expected display in the player?

On a different leg: I am pretty sure that Musicbee also allows to search for an artist and not just the album artist.

no the format string works. what I was truly trying to do, didn't work, that's to gather up everything by the artists under the artists name. well It does work, but looks super messy. all the albums become ripped apart, just like you said.

but yes I know about the search function, but every time I click an artist I'm not also writing in the name to see if they have tracks on soundtracks or compilations. would just like to have it neatly together.

If the display in the player is not satisfactory and there are no options to get it right, then I would seriously look for a better suitable player.
If nothing helps. Foobar2000 can be adapted to more or less any requirement ... but has a steeper learning curve to get it all customized.

In MusicBee, you can define what field you actually want to use. Check their support forum and Wiki, but this can be accomplished so that you see all tracks by an artist, even if they appear on a compilation.

Even without making any changes, you can use the search box and define to search by Artist rather than just Albumartist. This method even (unbelievably) works in iTunes as well.