Replacing that would be preferable. 1d6 cold damage is rather negligible except versus cold vulnerable mobs, of which there are a few such as fire mephits, fire elementals, fire giants, salamanders, and red dragons... but only against the first two categories will a mere 1d6 make much of a difference. Also there are just as many mobs immune to cold as vulnerable to it. I assume this damage is not multiplied on a crit and is just 1d6 no matter what; it just doesn't seem worth 3AP, rather it feels like an AP tax to get to the higher enhancements in its line. Look at it this way, any random generated weapon can have 1d6 cold damage added to it via Risia Festival crafting, no AP required, and with a little effort or plat that 1d6 cold could be icy burst instead... still no AP required.