With thanks to MrC, who has really done a great job in creating a script which may do most (if not all) what you need, you may wish to have a look at
thread: Change modified date after filename
specifically his last script, posted on 23 Aug 2013.
I admit, it is a bit of a tailor-made script and you need to test it first.
For example : your filename reads:
Filename 2011-07-29_082609.mp3
if you were to rename the filenames by removing the underscore (Filename 2011-07-29 082609.mp3), it will run just fine.
I have created a "Date from filename"-button to do the redates.
