Tom, you are correct in saying that Customs was separate from Excise until 1909.
To help others who may be working in this area, this is the history as I understand it:
a. Riding Officers (later termed Landguard) were created in 1690 to guard against illegal import and export of goods. They were mounted customs officers under the Board of Customs. Subsequently a small water based guard was added and known as the Waterguard.
b. In 1809 the Preventive Water Guard was created with the primary purpose being to prevent smuggling. This operated under the Admiralty.
c. Starting in 1822, the Preventative Water Guard, the customs waterguard and the Riding Officers were merged and named HM Coast Guard under the direction of HM Customs. It appears that most of the water based officers came from the Navy and most of the land based officers from the cavalry or police.
d. The detailed records for the Coast Guard for the period 1816-1947 are listed in the National Archives at Kew in ADM 175.
e. In particular, ADM 175 77 shows the “nominations” i.e. movements of personnel between coast guard stations in 1832 and has a distinctly separate section for “Mounted Guard”, which I presume is the term they used for the old Riding Officer title.
Much of the history is unclear and I may be corrected on the detail, but that is essentially what happened.
However, that is no help to me in my search. I specifically said that my ancestor joined the Mounted Guard in August 1832 and that I had him everywhere after that. I said that I was looking for where he was born.
I am concentrating on the Londonderry/Newtownstewart areas but as we all know, the Irish records are a challenge.
Tom, thanks for your interest.