If you are single, only your Conservator would have that authority.
What happens if my son needs his tuition paid while I’m disabled?
Again, if you haven’t planned, nobody can act for you until the court appoints a Guardian and/or Conservator for you. If bills, such as your son’s tuition, need to be paid in the interim, a friend or family member would have to use their savings or borrow to pay the bill.
What happens if my investments need to be changed quickly due to market conditions or to reflect new circumstances and risk tolerance?
A court would have to appoint a Conservator. Nobody but the Conservator would be able to act for you.