gv – Clause 51 (1e) of the NSW Residential Tenancies Act 2010 states:
That a tenant must not cause or permit a number of persons to reside in the residential premises that exceeds any number specified in the residential tenancy agreement.
So strictly speaking YES, your Agreement could be terminated by a heartless landlord, but why don’t you just ask the Agent to include an additional person on your new Agreement? Provided the numbers of occupants doesn’t exceed the number that can reasonably accommodated in the bedrooms, Agents generally just include those numbers on the Lease don’t they?
Perhaps contact Tenants NSW for some expert advice?
All the best for the arrival of your extra “tenant” 