Do you need a tutorial "How can I write a Filename-to-Tag Action"?
Hmm, I think, for you as a long time Mp3tag user it would be waste of time.
Regarding the technical aspect of your request the following Formatstring would be the closest approach. %DUMMY% - %DUMMY%, CD 0%TRACK% - %TRACK% - %DUMMY%
It will give
TRACK: 1 04
TRACK: 2 07
So in a second Action step the remaining space character needs replacing by nothing.
It seems that you should go completely the Action way.
My problem was that I couldn't get rid of the space between the two parts of the number, which I should have mentioned in my first post. But I believe that problem is now solved. Thanks to both of you.