Thanks for the link. I've just had a good dig through and it appears like reduced hours are only applicable under the JobKeeper scheme.

Working arrangements and the JobKeeper scheme Employers under the JobKeeper scheme can use the Fair Work Act >JobKeeper provisions to: *reduce an employee’s hours or days of work *change an employee’s usual duties *change an employee’s location of work. For information on the changes and how they apply to working >arrangements, see JobKeeper wage subsidy scheme.

Full-time employees (not on JobKeeper) still appear to need a new contract, or enter an agreement with the employer.

I have to be missing something here.