Action to affect multiple tags?

I've read pieces of posts that offer pieces of a solution here, but I just can't put them all together in my head correctly to come up with the answer for this specific situation...

I have thousands of files from VA comps that are terribly-named. (Thanks, bandcamp.) They mostly conform to the same convention...

TITLE: [artist] - [title]
ARTIST: V.A. [name of label that put out comp]

Conceptually, this is a simple fix:

  1. Overwrite ARTIST with the [artist] part of TITLE
  2. Delete the leftmost portion of TITLE up to and including " - "

From the reading I've been doing tonight, I am reasonably certain this requires creating a new, custom action, and the nature of the problem dictates the use of regular expressions. However, I can't seem to find an example using a regex action that affects multiple fields.

Can someone whose brain isn't as addled as mine seems to be help me figure out how to put all the pieces together into a coherent solution? Thanks.

If I understand you correctly, your use of [artist] and [title] does not mean that square brackets are actually used in the title.

in this case you could use an action of the type "Guess values".
Source: %title%
Guessing pattern: %artist% - %title%

You don't tell us anything about the filename. If there are title and artist in the filename it could also be possible to use the converter Filename->Tag.