Can you terminate employees because you need to save money (i.e. laying them off)?
It is not uncommon for smaller employers to fire a manager, and hire a new supervisor though. Same job - different title.
I'm unsure if it's been challenged at the FWC - I doubt it would stand.
So if you're reducing the number of staff employed to support "system A", but you have vacant positions supporting "system B", then you you need to offer those positions to any affected staff, or show why those employees would not capable of doing the new job.