The National Book Critics Circle is seeking to reinvent itself 46 years after its founding. Fifteen of its 24 board members, including the president, have resigned over a dispute arising from its attempt to draft a statement in support of Black Lives Matter. On Thursday, those remaining on the board announced several changes, notably efforts to diversify leadership that long has been predominantly white. The board has named an interim president, Jane Ciabattari, and announced that several of the awards it presents annually will be postponed or canceled until it makes “satisfactory progress” in diversity.