Looking to make a clean break with the past, some big-name companies spent millions on corporate rechristenings. Philip Morris Cos., the Marlboro marketer, had already sought relief from the anti-tobacco legions with a $180 million ad campaign that had little impact. So it went looking for a nondescript name instead, and found Altria Group (MO) Inc., derived from the Latin word altis, high. AOL Time Warner (TWX), trying to forget a romance gone sour, returned to its old-media roots with Time Warner (TWX). And WorldCom Inc., forced into bankruptcy-court protection by a monumental fraud, reverted to its MCI brand. Tyco International (TYC) Ltd. seemed ripe for a change, but new management chose to stand pat, for now. Turns out customers of ADT security alarms and Grinnell valves don't necessarily associate those brands with their troubled parent.