If you believe that the position they are now putting you in is not suitable and your position is redundant, then you can argue that they must give you redundancy.
Bottom line is that the law has held that inferior position is given to people as a redeployment in lieu of redundancies have been held to be valid and that they cannot seek further compensation.
Here is an information That may assist in your case where they have failed to be consultative in their decisions.
If you are not paid under award and your income is over $123,000 a year you are not entitled and fair dismissal applications and you would only be left with a breach of contract by the employer.
You would need to get further detailed advice from a solicitor the practices in employment and contract law to determine whether you have an action against your employer.
The fact that there is a substantive change in your position does not mean what they are doing is unlawful. If they are prepared to keep you on the position that is not lower paid then they are well within their rights rather than offering you redundancy.
If the aim is such where is a clear breach of the contract and designed to cause you to resign, your resignation would be a problem is you cannot bring an action for unfair dismissal.
Actions for breach of contract must be bought from the traditional civil courts which could be quite costly.
I know this is not a definitive answer but I hope it is giving you an idea of how the law operates.
Is there anything else I can assist you with?