...Is it so difficult?
You can mimic a sync...but it involves setting up a modification date field for every field in the database. And it has flaws, based on how filemaker fires auto-enter fields in related tables.
It is typically not advisable unless you really know what you are doing. A better course may be to create an Audit log. Then you could revert data back if there is a problem.
Ray Cologon has a nice example over at his site. http://www.nightwing.com.au/FileMaker/demosX/demoX01.html