If the change of call is permitted by the laws, then I can't see why law 16D1 shouldn't apply, and North may use the information that South would have bid 2
♠ over a natural 2
♣ overcall, but not over a support-showing cue-bid. However, something about this troubles me:
Quote
[L21B] Call Based on Misinformation from an Opponent
1. (a) Until the end of the auction period and provided that his partner
has not subsequently called, a player may change a call without other
rectification for his side when the Director judges that the decision
to make the call could well have been influenced by misinformation
given to the player by an opponent (see Law 17E). Failure to alert
promptly where an alert is required by the Regulating Authority is
deemed misinformation.
Was the decision whether to bid 2
♠ or pass really influenced by the failure to alert? Was South asked (afterwards) why they wanted to change their call?
I'm also not happy with the failure on the part of both sides to call the director. There is a common misconception that a late alert gives the next player an automatic risk-free opportunity to change their call; the director could have put them all straight on this matter if called on time. To some extent EW have colluded in the home-made ruling, but I might excuse them if they are particularly inexperienced.
I would want to ask South why the misinformation made them want to change their call, and why they felt they couldn't protect themselves by asking about the 2
♣ bid. I know they're the non-offending side and should be given the benefit of the doubt, but there are limits.