Question Author
Hi DG,
The question of injury does not arise, my question related to *voluntary* unforced change of wicket keeper at the captain's choice. As Everhelpful pointed out, there is nothing to stop any of the eleven players on the field (but not the 12th man [substitute] from keeping). In fact I have now found games where the keeper bowled, so Everhelpful is completely correct. My follow-up message jut pointed out that this could aid the fielding side to slow the game down considerably if that was favourable to them by changing keeper (therefore gloves, pads etc) after ever over, or in fact, after every ball! The reference you made to "nominated players" refers to any of the eleven fielders, and a fielder does not have to be nominated as a substute keeper before the innings commences - any of the eleven could be asked to take on this function.
Complicated game, cricket!
I imagine that no umpire would permit this under the "Ungentlemanly Conduct" law!
Thanks for your answer, anyway