There is no legal procedure for an arbitrary rerate (as the original poster seems to describe it) under USBC rules, and of course, it's being assumed that the league is USBC-certified.
A league has the option of many procedures (within the scope of its adopted rules) with regard to entering averages, and perhaps with regard to having to use previous season's average (for handicap purposes) for a certain number of early-season games.
But unless the league has adopted specific rules for average and/or handicap adjustment, there is no provision for arbitrary "changing" of averages and/or handicaps. And if a league rule adopted prior to the start of the season is to be changed, it must be done so with UNANIMOUS consent of all team captains.