I am not an expert, but it doesn't look like it.
Engine modifications are prohibited on provisional license:
https://www.rms.nsw.gov.au/roads/lic...finitions.html
Engine modifications must be certified on full license:
https://www.rms.nsw.gov.au/documents...ifications.pdf
How to get certified:
https://www.rms.nsw.gov.au/roads/reg...nstandard.html
From a cursory search of Reddit threads, it doesn't look like getting certified is an easy process even on a full license. Most exhausts don't even get certified.