Found some more raw data in the database about regrade charms. Added it to Item Grades.
Some interesting finds:
Downgrade Prevent Charm and Superior Downgrade Prevent Charm I assume aren't in the NA/EU version, or any version maybe. I don't remember seeing them.
There's 4 items yet to be put in any version of the game.
EDIT (3/18/15): The bottom 4 links are where the items will end up if they are eventually added to the game. Currently they link to nothing.
Item# 31978 and Item# 31979 provide and additive break multiplier of -50% and -100%, respectively (if there is a 60% chance of breakage, the first charm makes it 30%, the second one makes it 0%).
Item# 31982, I think, guarantees that it won't break. But if it fails, it guarantees downgrade.
Item# 31983 is the best. It guarantees no breakage or downgrade and provides an additive success of 1000% (if success is 3% it is increased to 33%).