About the GOP platforms:
The platform of the Republican Party of Texas is drafted by convention delegates, starting at the grassroots with resolutions at your precinct voting location, resolutions approved by each county/senatorial district, and concluding with a committee at the biennial Republican Party of Texas Convention, who combine the best of those resolutions (called "planks") into a single platform draft. Once the entire body of delegates make amendments to certain planks and approve that final draft, a new state platform is adopted!
The national platform is crafted via similar process: by a platform committee appointed by the Republican National Committee. This large committee takes into consideration the contents and the spirit of each of the states' and territories' platforms. National delegates may also amend and adopt the platform at the Republican National Convention every four years.