Filter to rename file based on days-since calculation

[Dilip]

Is there a Windows filter which would enable me to take a base date
and insert the number of days since that date into my filename? For
example, using January 1, 2010 as a base date, I would like to be able
to take a file named, say,

"20100103 (n days since Jan 1) - file name.xyz"

and rename it to

"20100103 (2 days since Jan 1) - file name.xyz"

Thanks!