UPDATE: Here is the full text of Sec. Tillerson's letter to Sen. Corker. It details some of the changes as follows:
The Ambassador-at-Large for International Religious Freedom (IRF) will continue to be an ambassador-level position confirmed by the U.S. Senate, and will be organized under and report to the Under Secretary for Civilian Security, Democracy, and Human Rights (J). Additionally, IRF will assume the functions and staff of the U.S. Special Representative for Religion and Global Affairs, U.S. Special Representative to Muslim Communities, U.S. Special Envoy to the Organization of Islamic Cooperation, and Special Advisor for Religious Minorities in the Near East and South/Central Asia.