If memory serves, its possible to password protect the macros in an
Excel book. If so, create a routine that only allows the book to be
opened upto a certain date. You'll have to hard code the date which is
why I raise the issue of the password. When I client requests a trial
copy you would go in, unlock the macros change the date, lock them and
send the file. Assuming of course that the password protect exists, its
been 3-5 years since I had to dig into Excel like that.