From what I understand, mp3tag doesn't edit folder names. For that purpose I use another program called Advanced Renamer.
I have a collection of folders where all I want is a particular section removed.
For example: Capitol Media Music The Professional 01 - Tom Elliot - Space Electronics (MERS-6)
What I want removed is the "- Tom Elliot" portion. All other folders that I want to rename follow this pattern, but the number of characters I want removed varies depending on the length of the artist name. I basically want to remove the name between the two hyphens, along with one of the hypens.
Advanced renamer also uses regular expressions and can remove patterns, but I don't know how to tell it to remove only the section I don't want.
Yes, Mp3tag can do that:
"Filenames" also includes "Foldernames" in this case.
If you use the backslash character \ within the new filename pattern, Mp3tag creates new directories below the current working directory for relative paths or at the at an absolute folder location if it starts with a drive specification, e.g., D:\Music .
MP3tag actually does.
See the documentation:
You could use Convert>Tag-Tag for _DIRECTORY
Format string: %album% - %publisher%
(assuming that
is stored in PUBLISHER).
The files inside the folders are not tagged yet, so pulling tags from them right now isn't going to work. Removing that one section from the folder names seems like a simple change. There's something I'm not getting.
Here's a visual of what some of the other folders look like:

In all cases I want the artist's name that's between the hyphens to be removed. Everything else can remain.
So,wouldn't that be the better first step: get all the data you can get from all the sources that are there (including the folder name) from the unstructured strings to the structured metadata fields and then clean the folder structure?
I would do it like that.
If you insist on fiddling with the OS property of a fully or partially qualified filename, then
I bet that program has also a forum.
If you're already using Advanced Renamer, isn't this what you want to achieve?
Text to be replaced:
\s-.*-\s
Replace with:
-