As the Boston Celtics transition from one ownership group to another, Brad Stevens suggested Wednesday that he doesn’t expect many changes to how his front office operates. A group led by Bill Chisholm reached an agreement last week to purchase the franchise from Wyc Grousbeck and the Boston Basketball Partners, LLC. Though Grousbeck is expected to stay on as the CEO and governor through the 2027-28 season, the Chisholm group will take over as majority owners this summer if the sale at an initial valuation of $6.1 billion is approved.