yup, redundancies can be used to dismiss employees. The caveat is that you can't rehire for that role for a certain period of time. This is simply to avoid the problem of companies claiming random employees are no longer needed.

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.

You also need to offer other options within the company if they exist.

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.