Yes, the rules are very strict - the succession is laid down by Acts of Parliament - laws passed by Parliament. Parliament can alter the order of succession - the Monarch can not.
In fact, it's not just the British Parliament that would have to agree - the Parliaments of every single one of the (at the moment) of the other 14 Commonwealth Realms would have to also pass laws to change the succession - and in Australia, the six state Parliaments would also need to do so - so you need twenty separate Parliaments agreeing to change the succession.
Relatively minor change was made to the laws of succession quite recently - to end male-preference primogeniture (where younger brothers took precedence over their older sisters) in future generations, and to remove the disqualification for marrying a Roman Catholic - and that took four years to happen, because of the need for all these Parliaments to take action.
Under current law, Charles will become King the instant the Queen dies. He could choose to abdicate in William's favour, but he would still be King until the Instrument of Abdication takes effect.
The Queen cannot change this herself. About the only situation in which it might change is if the Queen and the Prince of Wales both made it known that the Prince of Wales did not want to be King. In that cases, given enough time, I think it is likely that the Commonwealth Parliaments would agree to pass a law allowing that - but it's not something that is likely to happen right now - perhaps if Charles developed a serious illness (and remember he is in his seventies) it might happen.
Thanks NM, I knew you would have the facts as they are. I knew the Queen couldn’t just up and change the order of succession on her own. I had no idea what it would take to make such a change.
Personally, I hope Elizabeth can carry on for a good while longer. I admire the Lady.
I hope things are going well in Oz. Y’all had a tough time with the COVID lockdowns. Hope you get back to normal soon.
Thanks!
I am currently reading Dickens’ “A Child’s History of England” and find it very interesting!
Succession was handled mostly via sword and executioner’s axe back in the day...................