Could you pl provide a link to the application to join the Civil Service in 1867
British Civil Service Evidence of Age
https://www.findmypast.co.uk/transcript?id=GBOR/CSEOA/00037885"I Daniel McNeill of Larne in the County of Antrim, Flesher, do solemenly and sincerely declare that my Son John McNeill nominated for the situation of Rural Post Messenger was born on the Second day of November 1848, and is now above 18 years of age."
And I make this solem declaration conscientionly believing the same to be true.
Declared at Larne 10 Jan 1867 by declarant Daniel McNeill (X his mark) and signed by a Justice of the Peace taking the declaration. Witnessed also by Postmaster James Reath.
Accompanying note with 1d Inland Revenue stamp attached.
"I have examined and find that John M'Neill Son of Daniel M'Neill and Rose Barry was baptised in November 1848" Francis W Kenna, PP [Parish Priest] Larne, Jany 7, 1867.
I would therefore say you are
conflating 2 totally disparate events different fathers, occupation and religious denominations, although which one is valid for your tree is unclear. Perhaps need to work back again from the 1901/11 census using his children to confirm mother's maiden surname and denomination and verify/locate the correct marriage entry. Or just discount this Civil Service application.
The register for the 1848 is missing on NLI
https://registers.nli.ie/parishes/1142 It could be in PRONI, they only give an overall range in their guide.
but "It was not until 1852 that Larne and Ballygowan became separate parishes and the first church was built by Fr Arthur O’Neill on the site of an old disused slaughterhouse in 1831 and basically this is St MacNissi’s today.
Two priests in particular, figure high in the development of Catholicism in the town of Larne - Fr Francis McKenna, parish priest here for 41 years in Victorian times"
https://www.facebook.com/MacNissi/posts/this-article-was-published-in-the-larne-times-on-june-9th-2009st-macnissis-churc/839407006107731/Consulting eCat whilst the period is missing in MIC1D/68 it seems to to present in MIC1D/90/1
Description:1828-83: Copy of a register of baptisms 1828-83; and of marriages 1828-82. Up to Easter 1852 the entries relate to the Roman Catholic parishes of Larne, Carrickfergus and Ballygowan.