Except as otherwise specifically authorized in this section, whenever a vacancy occurs in the grade of colonel or higher in the South Carolina Air National Guard, it must be filled by promoting the officer of the next lower grade in the South Carolina Air National Guard who is fully qualified for promotion and who is, in the opinion of the senior tactical Air National Guard commander, the chief of staff, headquarters, South Carolina Air National Guard, and the Adjutant General of South Carolina, considered to be best qualified to fill the vacancy notwithstanding seniority among those officers qualified to fill the vacancy.