DirDate is a command line tool that can easily be automated to change files' last modification date, creation date or last access date.

It can change dates using either a reference file (where you can 'lift' the date from an existing file), the current date/time or a series of YEAR, MONTH, DAY, HOUR, MIN, SEC and MSEC commands.

It can process files in subfolders, handles read-only files and it has a preview mode so that you can see which files will be modified.