Well, if it were to 'somehow' be locked, i.e.: upon saving, you may
inadvertantly lock it as well. There will be something that you will need to
do to the file, either typing in the date in a cell, or using a naming
convention for the file name for a copy of the file, in any case. The
advantage of the naming convention that I have suggested, is that if you also
keep a history of all the 'old' files, then if there is ever any question,
you do not have to recreate any of the older versions, just open the one with
the approrpriate date.
Just my 2 cents.