Changes in the company's managerial structure raised concerns in the market.A pair of executive resignations led to a mild sell-off in Advance Auto Parts (AAP -0.51%) shares on Friday. The company's stock closed the day 0.5% lower on the news, on investor concern that the company's managerial structure might not be entirely stable. By comparison, the benchmark S&P 500 index landed in positive territory by rising 0.9%.Double resignationBefore market open that day, Advance revealed in a regulatory filing that ...