A way to alter the prefix of the EML filenames

A way to alter the prefix of the filenames when converting to EML files.
Now the format is fixed to .__

But I don't like the added index number, since that does not always match the true order of the mails by date!
And as I would like to see the EML files being sorted by date, and thus the ISO-dateformat (yyyy-mm-dd) should be used for that instead of the dd-mm-yyyy format.