There is no way to prompt for anything while executing actions.
See e.g. here:
If you want to use varying expressions, Convert>Tag-Tag may be an alternative. In "Manage History ..." you can set names for format strings and so retrieve them easily.
Or, the use of a filter would also be an option to limit down the number of files to match the set parameters.
As you do not give a real example of the data, I can only suggest in general that perhaps the currently used expression is not the best for the purpose, e.g.
$regexp(%title%,\d+\s*,) would remove any leading digit.
But to get a better format string would require a real example.