>There is an ability to apply the change to the existing records, as I recall. Check closely ALTER TABLE syntax for the WITH CHECK clause.

I do not see anything in there which negotiates with that:

WITH CHECK | WITH NOCHECK

Specifies whether the data in the table is or is not validated against a newly added or re-enabled FOREIGN KEY or CHECK constraint. If not specified, WITH CHECK is assumed for new constraints, and WITH NOCHECK is assumed for re-enabled constraints.

If you do not want to verify new CHECK or FOREIGN KEY constraints against existing data, use WITH NOCHECK. This is not recommended except in rare cases. The new constraint will be evaluated in all future updates. Any constraint violations suppressed by WITH NOCHECK when the constraint is added may cause future updates to fail if they update rows with data that does not comply with the constraint.

Constraints defined WITH NOCHECK are not considered by the query optimizer. These constraints are ignored until all such constraints are re-enabled using ALTER TABLE table CHECK CONSTRAINT ALL.