You could automate this by running an export as FileMaker that includes the field(s) to be changed as well as the PRIMARY KEY, modifying the field(s) in the exported file, then do a matching import (using the primary key) and NOT allowing Auto-Enter fields to update (the dialog following the import-matching dialog). That will change only the field(s) you modified, without allowing auto-enter values like Modification Date to change.
One note of caution: If any of the imported fields are used as the source-side of a lookup, the lookup values will re-lookup. In your example, if you had any fields that do a lookup based on the Country Code, then those fields will re-lookup based on the (now correct) country code, even though you did not enable auto-enter. This may or may not be what you want to have happen, but you need to be aware.