
Britain will see a wealth of modifications to everyday things as the Queen’s picture and logo on banknotes, letterboxes and stamps are replaced with that of the new King, Charles III.
British money won’t be replaced overnight and the transition will take years as new coins and notes are created with the face of the King and the others are slowly withdrawn from circulation.

Another change will be that while the Queen’s picture faces to the right on coins, new ones will show the King facing left. This is due to a practice dating from the 17th century to alternate the way successive sovereigns are facing. The Queen’s coin didn’t emerge until 1953, the year after her accession.
Until British money was decimalised in 1971, it was common to see multiple monarchs facing both ways, in a handful of change.

The new coins and notes will need to be designed and minted or printed. Then The Royal Mint advisory committee must send recommendations for new coins to the Chancellor and get royal approval. Designs are then selected and final choices approved by the Chancellor and then the King.
Stamps also display a picture of the Queen and new ones will have to be created featuring the face of the King, again with the existing ones phased out slowly. Charles may have already sat for such sculptures or pictures, and he will again have to approve the designs.

Royal Mail postboxes bearing the Queen’s ER cypher (for Elizabeth Regina, the Latin for Queen) are unlikely to be removed. In fact, some embellished with the Queen’s father King George VI’s GR (George Rex, Latin for King) cypher can still be seen today, but any new postboxes could feature the new King’s insignia.
A representative for Royal Mail said that following the death of HM Queen Elizabeth II, Royal Mail has confirmed that stamps carrying the picture of Her Majesty Queen Elizabeth II remain valid for use. These include definitive stamps, regular everyday stamps, and special stamps, and as previously announced, following the introduction of barcodes to everyday stamps, these stamps remain valid until the end of January 2023.
All special stamps that have already been announced will be issued, although the takeoff dates of some may alter, and in line with past practices following the demise of a sovereign, all current post boxes will remain untouched.
Postboxes already in production or being prepared for installation will also maintain the seal of Queen Elizabeth II.
In criminal court cases, the R to denote the Crown now stands for Rex rather than Regina. Another change in matters of law is that barristers and solicitors appointed by the monarch will see their title switch from Queen’s Counsel (QC) to King’s Counsel (KC).
However, things like this should be replaced when they need to be through wear and tear or expiry because public finances shouldn’t have to bear the expense of tradition, although wear and tear on a post box would take decades. However, we do live in Great Britain, not Little Britain, but still, there’s no need to squander money on things like this and there’s definitely no hurry.
But then I guess this is minor compared to the incompetence of Parliament during COVID wasting hundreds of billions of pounds, and I suppose tradition is what makes Great Britain.
The thing is it really makes no difference because ultimately letters and stamps will become extinct, along with money, and I truly hope that King Charles III has a good inning or it will end up costing us a fortune.