Expense is, and always was, a major consideration regarding uniform change at the accession of a new monarch. I am confident that change will be slow, we are talking big money for change before items wear out.
Time was [c. 1903] when the Foot Guards had two scarlet Home Service tunics [band had three], and an undress tunic [little known and seen, worn in barracks], a special pattern scarlet frock [also barracks], a white drill jacket, and two suits of khaki service dress.