As an idea it was stated policy from the Iraq Liberation Act (which did not justify war to those ends). Regime change was apparently the desired end of US soft power, regime change was not sequestered away in the vault of a right-wing think tank until Bush came in. Policy does not become a blank slate as soon as some sinister neo-cons sieze control and trick the entire nation into believing Saddam had WMD, there were ten years of WMD justified sanctions, bombings and attempted coups that simply don't go away because of Bush or the war.
regime change does not equal invasion and occupation. everyone wanted regime change. the discussion was about how to do so, and it was only in the far right/neocon closet that the actual overthrow via military might was discussed. assassination, working with Iraqi dissidents on the ground, etc., all this was on the table. only a few thought that it was worth any time or effort.