The power/toughness-setting effect overwrites other effects that set power and toughness only if those effects existed before this spell resolved. It will not overwrite effects that modify power or toughness (whether from a static ability, counters, or a resolved spell or ability), nor will it overwrite effects that set power and toughness which come into existence after this spell resolves. Effects that switch the creature's power and toughness are always applied after any other power or toughness changing effects, including this one, regardless of the order in which they are created.