You may have a serious issue with this.
Changing the password will in some instances not affect anything because it is the security token being passed around the system and not the password. If it is Trusted connections only then again you will be OK to change the password.
But if you have mixed authentication and (load processes, extracts, automated anything) then you need to be very, very, very, very, careful!!!!!!! I suggest that you run profiler for a good week+ to see what accounts are login before you change the password. I have come across applications that were installed under SA privs and the only way that the SA password could be changed was to reinstall the app. You will also not immediately know whether or not a once a month business critical process requires SA.
Good luck, and walk softly