You may apply an action "Guess values" with a fitting pattern, which may vary depending on the given format of the TITLE string.
Action "Guess values"
Source format: %TITLE%
Guessing pattern: %COMPOSER%:%DUMMY%
From:
TITLE = Verdi: Preludio Atto I (La Traviata)
To:
TITLE = Verdi: Preludio Atto I (La Traviata)
COMPOSER = Verdi
See also ...
https://www.google.de/search?q=site%3Aforum...de+Guess+values
For a sophisticated example see there ...
/t/12651/1
DD.20150720.1718.CEST