At first it seems straightforward. It is a lead out of turn, and the laws allow LHO to accept a lead out of turn. It's pretty clear: Law 53A "Any lead faced out of turn may be treated as a correct lead."

The problem is, the laws also say that dummy cannot choose a card to play. Law 45D: "If dummy places in the played position a card that declarer did not name, the card must be withdrawn if attention is drawn to it before each side has played to the next trick."

So you have two straightforward laws that seem to contradict. I am pretty sure that Law 45D takes precedence.

However, until the opening lead is made, the to-be-dummy is not the dummy. The definition of dummy: "Declarer's partner. He becomes dummy when the opening lead is faced." So, does Law 45D apply or not?

Law 54C is also relevant. This concerns when an opening lead is faced out of turn. The laws clearly intended this to apply only the defender's opening lead out of turn, but in the headless chicken department: "If declarer could have seen any of dummy's cards...he must accept the lead." That seems to deny declarer the right to change the play of a card dummy has selected.

One opinion: David Stevenson said "Less clear is whether the opening lead has to stand." This was after discussion of this on a messageboard. I don't think anyone disagreed with his opinion.