It did happen to me on my application. Before you change your job, you need to ensure that you're still in the same field with your assessment result (I presume you're applying on 175 Skill Independent Visa).
For me, when CO assigned on my case, I updated him with my new job or employment even on my case I also updated my living country (I move from Indonesia to Singapore during my application). Eventually you will need a document (reference for your employer) or a legal statement letter that you're still working on the same field with your initial submission.
Actually, it had been stated in DIAC document when they receive your submission. I excerpt it below.
[B]Changes in circumstances[/B]
If an applicant’s circumstances change, such that an answer in the application form or supporting information is no longer correct or is incomplete, you must inform the Adelaide Skilled Processing Centre in writing as soon as possible.
Examples of a change in circumstances include changes to:
. address and/or contact details
. employment eg a new job
. new passport
. new member of your family unit
. discovering information provided in the application is incorrect
You can provide this information to the Adelaide Skilled Processing Centre by writing a letter or e-mail and sending this, along with any accompanying documentation, to this office.
If you are notifying a change of e-mail address by sending an e-mail from your new address then you should also include details of your previously authorised e-mail address in your correspondence to enable this office to be satisfied that you have authorised the change.
Alternatively, you can use forms specifically designed to allow you to notify the department of changes to your address, circumstances or application form answers. For information on departmental forms please refer to the department’s website Department of Immigration & Citizenship and refer to Finding and Using Forms and Booklets (Applications and Forms - Visas & Immigration)
The following forms are useful for notifying changes in circumstances:
Form 929 Change of address
Form 1023 Notification of incorrect answer(s)
Form 1022 Notification of changes in circumstances
Form 1193 Communication by E-Mail with the Department