Q. If I change my method of storing attached files from database to hard drive, will this automatically put all existing files on my hard drive?
A. After you switch the attachments storage method from the database to a disk only new files will be written to a disk, files added using old (DB) method will stay in the database.
But, there's a way to move all files to a disk - you can copy projects (using the "Duplicate project" feature) and then delete the original ones.
Note that time entries are not copied along with projects.