Recognize if user has changed own profile values

We need a possibility to recognize if a user has changed his profile details. Reason: We want to sync the WP users DB with an external shipping tool where we ship goods. We sync both databases via putty and a ssh login. Now we need to have a way for the shipping system to check if there had been changes on several users (last-user-changed-date / set a flag when user data has changed).

Does anyone have an idea how to accomplish that?

My second question: What happens to the WP DB during an Update, when there are additional tables or columns in a table that do not belong to WP? Does the update drop this columns or are they update-safe? We need them for a syncing info, too.