Mark M. Weinstein has been named senior VP of government affairs at Viacom International Inc., a unit of Viacom Inc.Weinstein, 50, whose appointment is effective Feb. 1, had been senior veep and general counsel. His successor will be named shortly. Weinstein will be responsible for public policy issues affecting the company from a Viacom office soon to be opened in Washington. The move puts Viacom squarely in the middle of renewed governmental regulation of the cable industry. Weinstein will represent the company before Congress and the Federal Communications Commission.