right the column of the ItemInfo.shn has a section for enhancements and the max limit of +10 to +11 you might consider Karis also. I will show you the columns that you require to modify.
UpLimit ~ change to 11 to make it +11 enabled
UpSucRatio / UpLuckRatio ~ 10 = 1% so to make it easier not to break you would have 1000 in them.
@MrFarbodD is correct with the Quote
Code:
AccUpgrade.shn (for accessory) and ItemUpgrade.shn (for items).
however, you still need ItemInfo.shn modifications which i've stated above.