The King had no need to declare young Barack Jr. a citizen of the British Empire. He was one at birth.
Only because that was the statutory (or perhaps constitutional) law of the Kingdom at the time of his birth.
The manner in which citizenship is bequeathed (how it's codified) is probably immaterial. The fact is that is codified somehow, either through the country's constitution, common law, statute, or case law.
The logical rub here is that one cannot be a Natural Born Citizen of anywhere by statute. BHO, Jr. Becme a “dual citizen beause of his parentage. BHO, Sr. was a Natural Born Citizen of the British Empire, passing onto his son the rights and privileges thereby.
The King had no need to declare young Barack Jr. a citizen of the British Empire. He was one at birth.
From William Rawle’s book “A View of the Constitution of the United States of America” (1825) which was quoted in the Congressional debate of the 14th Amendment as well as as by the Supreme Court of Connecticut in the case of the Town of New Hartford v. The Town of Canaan (1886): “The citizens of each state constituted the citizens of the United States when the Constitution was adopted. The rights which appertained to them as citizens of those respective commonwealths, accompanied them in the formation of the great, compound commonwealths which ensued. They became citizens of the latter, without ceasing to be citizens of the former, and he who was subsequently born a citizen of a state, became at the moment of his birth a citizen of the United States. Therefore every person born within the United States, its territories or districts, whether the parents are citizens or aliens, is a natural born citizen in the sense of the Constitution, and entitled to all the rights and privileges appertaining to that capacity.”
William Rawle was appointed by George Washington to be the first US Attorney for the District of Pennsylvania.