Heres the reply I got..
Dear Lindsay,
Thank you for your query regarding learner riders in the ability to be
able to ride within Centennial Park (CP) through CP Info.
The regulations do say learner drivers are prohibited from driving in
(CP).
The regulations do not prohibit learner riders from riding in CP.
In regards to removing learner plates from motor vehicles this is not a
subject I can help with you should refer that to the Roads and Traffic
Authority.
If I can be of any further assistance please do not hesitate to contact
me on 9339 6615 or email david.caple@cp.nsw.gov.au.
David Caple | Senior Park Ranger
Locked Bag 15, Paddington NSW 2021
t. (02) 9339 6615 / 0407 225 564
And kiwiscoota is correct...it's on the myrta website...no learner riders in the parks grounds