VATICAN CITY — Pope Benedict XVI on Monday changed the rules of the conclave that will pick his successor, allowing cardinals to move up the start date if they all arrive in Rome before the usual 15-day waiting period after the end his pontificate.

Benedict signed a legal document, issued Monday, with some line-by-line changes to the 1996 Vatican law governing the election of a pope. It was one of his last acts as pope before stepping down at 8 p.m. Thursday.