I looked around in the support threads, but was likely using the wrong search terms.
My new car does not display the album title on the dash screen. I'd like to be able to see that info. The idea is to combine the artist and album title in the album artist field. Pretty sure the regular expression action will work here, but I don't have any other actions that are similar so I can't modify one I already use. The closest I have is Format value "ARTIST": %_parent_directory%, but that clears what is in the field already.
I plan on manually adding the artist name as an abbreviation (if the name is long), then clicking this new action to add the space, a hyphen, another space, then data from the Album field. Like this: " - ALBUM"
The result for album artist field should be: Agent Orange - When You Least Expect It
No regular expression required here. Just use the Format Value action.
Format String: %artist% - %album%
Note that this is not really ideal, as this will impact how your library works for other media players that have better tag field support. Keep that in mind before you mess with your original library. I would consider copying the files you want to use in the car to a separate device first. Then use mp3tag with the above action on that device only. This will keep your original files intact.