Thanks for getting back to me Sinead. I'm certain there was no reason to hide from authorities by changing his name (and I have a few convict rels so I'm not squeamish about the possibility ;-D).
I thought I'd pass on some information I have gathered in case others are interested. Thomas certainly had a tough life in Australia - but of course almost everyone did in those days.
According to a ship's book (not logbook) listing arrivals to Sydney, Thomas was an Agricultural Labourer aged 22 at the time of application but had turned 23 by the time they sailed. Catherine was listed as a farm servant on the ship's log. James Edward (was he a Kearney or was Edward his surname?) and Mary Calive both of "Lismaladuff" certified his character and person. One was a relative as was the regulation then. His "state of bodily health and probable usefulness" was listed as "good".
They were also listed as Roman Catholics but neither had a certifying registration of baptism.
The fare was £19 each and they were sponsored by John Miller.
Both Thomas and Catherine were illiterate. Both parents were living.
There were 284 emigrants and 14 intermediate passengers on board the ship. There was an outbreak of smallpox on the ship with some passengers dying during the journey.
Two of Thomas' daughters were also said to have died on the way out but 6 month old daughter Sarah survived.
On arrival to Sydney Town there were 23 passengers ill, so they were all put into quarantine until their release on 23 Oct 1841.
The family settled in Port Macquarie in NSW for a while before Thomas selected land at Gannons Creek, well out of flood reach. However, this meant the soil was the poorest so Thomas had to work away from the area for weeks on end clearing land and working on road building across the New England ranges.
In 1861 Thomas had the contract to take the mail from Huntingdon to Port Macquarie. He made the return journey once a week by horseback for the sum of £28 a year.
The Carneys also made cheese for a while, milking about 35 cows once a day. The cheese was sent to Sydney by boat from Port Macquarie and when it was time to go to Port to catch the boat, they had to leave Gannons Creek about 2am with the cheese loaded on a packhorse.
However, there was a sudden flood one night and the calves were washed away and drowned. The cows fretted, their milk dried and that was the finish of the cheesemaking.
On 1st February 1891 a non-official Post Office was opened at the Carney home at Gannons Creek with Thomas Carney Snr as Receiving Officer. In this position he was paid an allowance of £5 per annum.
Catherne died on 15 Jul 1901 aged 85 years and Thomas Snr, aged 86, followed on 4 March 1903. They are all buried at Beechwood Catholic cemetery.
A relative has said that Thomas or his family owned flax mills in Ireland. Not sure how I would verify that.
It's said that his father's name is Edward (b1793 -?) and mother Sarah (1804-1842)
Also I don't know how to go about contacting the parish priest for his birth details. Do you have an address please?
Thanks for your help with this,
Robbie