Still no doctors, but consensus seems to be – as far as general public knows – DON’T DO IT! It is irreparable damage. One of the things I know for sure, is that during the labour, if doctor sees that mom will not be able to stretch enough and that there is possibility that she would tear, doctor makes the incision, so to ensure that the tear will not go in the direction of sphincters – for that simple reason – that the damage is permanent.
With regular enemas and but plugs – that particular function can be brought under pretty strict control – to the point where one will not be able to move bowels without enema – and just to get that fixed is painful process (not recommending – just mentioning that there are other way that are not necessarily causing permanent damage).