In a letter to KALD (Houston Christian Broadcasters) the FCC clarifies the licensee's requirement of maintaining original service area based upon a 307(b) preference filing.   

When non-commercial applicants apply for a new facility in a group of competing applicants, usually the tentative selectee of a construction permit is either based upon the NCE point system, or superceding criteria based upon claiming first or second radio service to a new population location.  Because a applicant can trump by claiming 307(b).  However, the FCC is now stating the applicant cannot submit a minor modification to abandon service to an area claimed in the original application, even if the applicant proposes to serve an additional underserved of equal population in the modification.  Such notice is verification that if an applicant proposes to serve an underserved area on its original application in order to win a specific channel, they must adhere to building that proposal.

Letter to KALD (FM) from FCC