Can someone help me with some related but slightly different problems?

1) Is there a function that will detect whether or not a cell has been
changed since a spreadsheet was opened? If so I can use this to prompt a
user to increment a version number in the file, which in turn will prompt
them to save the file to a different file name.

2) That's my simplest hope. If not, is there a method of automatically
incrementing a version number when a file opens? This would also mean I
would have to somehow force the user to save the file to a different file
name, since it would not be immediately obvious that it has happened (if you
see what I mean). Can this be done?