I have over 20 years Property Management experience in the…

I have over 20 years Property Management experience in the Western Suburbs of Perth and I commenced my current employment on 21/04/16 and am still employed with the company. I signed an ‘Employment Agreement’ at the beginning of my employment.
My official title written on my Agreement in Annexure A – Job Description is ‘Senior Executive Leasing Manager & Business Development Manager (Claremont). Claremont is the suburb / area where our office is situated.
In the Agreement Clause 3.2 titled ‘Job Description’ it states:
(a) A job description outlines the duties of the Employee which are in excess of those duties set out in clause 3.I, is set out in Annexure A.
(b) The Company may vary or amend the Job Description from time to time in its absolute discretion, provided the Job Description remains within the reasonable competence and qualifications of the Employee.
Clause 19 of the Agreement titled ‘Variation’ states:
‘No modification or alternation of the terms of the Agreement is binding unless made in writing dated subsequent to the date of the Agreement and duly executed by the Parties’.
I went on annul leave for 2 weeks end of January this year however I was involved in a motor accident during my annual leave period and ended up taking extra time off as sick leave and unpaid leave.
When I returned to work I was told in passing (not in a meeting) nor was it put in writing, that they had employed a full time Business Development Manager and I would no longer be required to fore fill this part of my job description. This directly affected my earning capacity as I earned extra money with each new management (new business) I brought into the company.
My question is, can my work place legally change my job description without written notification or mutual agreement, effectively altering my earning capacity with no offer of compensation?
In saying this, I have no objection to my work employing a full time Business Development Manager as it gives me more time to service my existing clients. However I would like to think that I could still keep my Business Development (Claremont) title by servicing existing clients via our sales reps and still be remunerated. I just wouldn’t actively be sourcing fresh new business that is not connected to any of the sales reps.
Any advice on the matter would be greatly appreciated.

Lawyer's Assistant: Because family law varies from place to place, can you tell me what state this is in?

Wa

Lawyer's Assistant: Has anything been filed or reported?

No