Manage change in employee class in HR module

We have the situation where and employee can change from a class of contract employee to full-time and vice-versa. HR wants to be able to track the date where the class changed. Would this require 2 separate records for these employees? The system will not allow 2 records to thave the same SSN, so we would need to put in a "bogus" SSN for the non-current employee record. Anyone else have this situation.

Please Advise. Thanks

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