The magic weapon special ability changeling (Compendium of magic objects 31) (2,000 in., 0 lb.) – and other special abilities with a magic weapon at a flat fee – do not count as magic enhancement bonuses and are not equivalent to magic enhancement bonuses. These special abilities of magic weapons at a fixed price do not generally affect the cost of weapons. other The special abilities of magic weapons, whether these special abilities exist or are added later.
To be clear, nothing says that such lump-sum capabilities make count as a magic enhancement bonus – and no way is given to determine the cost of a magic weapon if such abilities are considered magic bonuses – so , by default, such special abilities for magic weapon at fixed price do not count as magic enhancement bonuses. (In a game based on exceptions like 3.5an exception for such capabilities should be clearly defined for it to apply.)
However, a weapon must still have at least a +1 magic enhancement bonus so that such fixed cost magic weapons can be added to it. In addition, these special abilities of lump sum magic weapons count to know whether a weapon is considered epic or not (see Compendium of magic objects on the properties of the weapon (28)).