To summarise.
Though someone else may be able to do it better than me.
MNHQ allowed a regular mumsnet poster to carry on with a thread they knew to be a wind up yesterday.
Today they have changed teh MN Talk Guidelines on trolls.
Their previous rules, which were valid yesterday, stated that they do not allow trolls including those that do it just for the hell of it.
Today, they are have changed the rules. And have quoted them, so it looks like the MN poster who started the thread yesterday, did not break their rules.
They have also not stated that their rules have been changed, either today, or in the last few hours.