Having two - or more - official jobs was by no means unusual.
Both attendance officers and registrars were appointed by the Tendring Board of Guardians. The attendance officer, like the relieving officers, were paid by the board, but registrars lived off their fees. Quite what the various roles of the Registrar General, Superintendent Registrar, and guardians were in the appointment process is not entirely clear. That's especially so where the boundaries of the poor law union and districts didn't align, and kept changing as new housing was built.
The Tendring guardians had a lot of business in this regard from 1900 on. In 1900 the registrar for births and deaths lived in Thorpe-le-Soken, and was also the relieving officer (and vaccination officer and collector of the guardians). Note that the vaccination officer mentioned here was not the public vaccinator. That was a job for a doctor, while the officer looked after the paperwork and enforcement of the rules requiring vaccination.
Clacton Urban District Council started demanding their own registrar and and assistant relieving officer, and a complicated argument ensued. At one point the RG declined to divide the district, as compensation for loss of fee income would have to be paid, but if the post fell vacant he would think again.
And the incumbent did vacate the post in early 1902, to become relieving officer in Croydon, but the division didn't happen then. The guardians advertised the vacant posts of relieving officer, vaccination officer, collector of the guardians, and registrar of births and deaths, but made clear (if not explicit) that a single holder was expected. Payment was partly by salary but mainly by charging fees, with an estimated total of £175 pa. The fact that this would fall significantly if, as was expected, the extra posts were created, was known at the time.
The RG intervened before confirming the chosen candidate as registrar, so this Mr Folkard had to agree to this division. Then a new selection process was conducted for Clacton and St Osyth, and the post given to Morris Constable in October 1902.The next year Folkard was asking for a pay rise on the grounds that his salary as relieving officer was lower than others' because of his expected fee income.
Mr Constable died in 1904, and this time the guardians voted to appoint his widow, who had shown her competence by deputising in the interim. Note that she had been officially appointed as her husband's deputy and so was acting "according to the regulations", showing that this label of deputy registrar, or deputy to the registrar, was used in conflicting senses.
It's also worthy of note that the secretary to the board of guardians, Mr A J H Ward, was the Superintendent Registrar for Tendring district, as well as being a solicitor in Harwich. And, in 1900 the RG wrote to guardians suggesting that they "should,. as far as possible, allow their officers to act as enumerators as being likely persons to take an intelligent interest in the work, and see that the papers were filled up correctly."