Paigntonian and others, //Further to earlier contributors I find the sudden re-writing of leadership rules curious. Did the '22 meet in secret this morning and agree on a new Tory constitution? Did they meet after Truss' resignation? Did Brady write it on the back of a fag packet?//
None of the above. This article, published three days ago, is behind a paywall but there's enough of it that's readable to explain what happened.
https://www.independent.co.uk/independentpremium/uk-news/liz-truss-remove-tories-1922-committee-b2205326.html
//Senior members of the powerful 1922 Committee of Conservative backbenchers are said to have held secret talks to discuss the possibility MPs will soon demand Liz Truss is replaced as prime minister.//
In other words, her removal was anticipated - which is hardly surprising.