The problem is the GOPe can change that rule prior to the convention.
The Republican National Committee may, by three-fourths (3/4) vote of its entire membership, amend Rule Nos. 1-11 and 13-25. Any such amendment shall be considered by the Republican National Committee only if it was passed by a majority vote of the Standing Committee on Rules after having been submitted in writing at least ten (10) days in advance of its consideration by the Republican National Committee and shall take effect thirty (30) days after adoption. No such amendment shall be adopted after September 30, 2014.