lamford, on 2017-September-20, 06:27, said:
My understanding is that if offender chooses a replacement call that has a meaning that is one that could be attributed to the withdrawn call, it counts as a comparable call. So if they replace it with 2♦, that's a transfer to hearts and has a similar meaning to a 1♥ opener, that's a comparable call. (It would also be the lowest legal call that shows hearts, so allowable under law 27B1(a).) If they replace it with 2♥, that's a transfer to spades which is also a meaning that could be attributed to the heart bid (if they were trying and failing to make a transfer), so that's also a comparable call. I'm not sure how far this should be stretched to allow your other suggestions.
There's a presumption that offender won't take advantage of this by showing one hand type with the first call and another one with the replacement call, and so get two bids for the price of one. If they did, partner would have to be able to work out what they were doing to gain an advantage, and if they did gain an advantage, they'd be likely to lose it under law 27D anyway. I've not seen this aspect of the law fully road-tested yet, and I'd be interested to see how it works out. I had a couple of promising-looking starts at the Eastbourne Summer Meeting, but they didn't go to completion because the illegal calls were accepted.