Will immigration SA will update my nomination application without my consent if someone else send a mail with my application Id

I have this complicated scenario. Please share your advice, I really appreciate your support.

I initially contacted a migration agent, where they created an EOI (after paying their fee), but I do not have access to this EOI.

However, I also created an EOI for me, and during the SA nomination application, I submitted EOI number I created (I submitted the application by my self because agent had so many candidates to submit).

My agent has a PDF copy of my SA nomination application, with my application ID (he requested it so I shared a copy). My application is still in the submitted stage.

I am not satisfied with the service the agent provides, so now I am thinking of going ahead without this agent. My concern is, after he got to know my decision, he might get angry and might try to harm my application in any possible way.

So, if the agent send a mail to immigration SA, referring my application Id, asking to change any information(specially the EOI number) in the application, will SA consider it without re-verifying with me? Or will they verify the email came from different address and contact me before taking any action or at least will SA notifies me?