As I understand it, an employee has a contract.
That contract can be varied by agreement.
If there is no agreement, what happens?
If there is a workforce reduction, then you would be in a redundancy situation. If a role was removed, say the CSD, this would also be a redundancy situation.
A variation of a contract is not a redundancy. If you terminate and re-engage, you are being dismissed and may be able to seek unfair dismissal.