The rule the RNC changed was "40b" which states:

(b) (1) For the 2016 national convention, each candidate for nomination for resident of the United States and Vice President of the United States shall demonstrate the support of a majority of the delegates from each of eight (8) or more states, severally, prior to the presentation of the name of that candidate for nomination. Notwithstanding any other provisions of these rules or any rule of the House of Representatives, to demonstrate the support required of this paragraph a certificate evidencing the affirmative written support of the required number of permanently seated delegates from each of the eight (8) or more states shall have been submitted to the secretary of the convention not later than one (1) hour prior to the placing of the names of candidates for nomination pursuant to this rule and the established order of business.