Here is some experimentation of mine :
05 = Orb/Crystal
06 = Blade/Katana
07 = Great Sword/Daikatana
08 = suit
09 = glove
10 = boots
11 = helm
12 = helm (again?)
15 = ring
16 = amulet
17 = epaulette
19 = unknown (0.O, i mean the word "Unknown" is displayed as item name)
22 = board or bike (!!)
24 = COATING KIT
27 = "spetial potion"
28 = (?) helper T message (?)
29 = slot extender
31 = craft lvl stuff (item for craft lvl rank up)
32 = earring
33 = bracelet
35 = core enhancer
38 = fast dc, but guess some kind of costume
43 = recover some kind of penality ("no more penalty to recover" when i use)
44 = change kit
45 = rename card (make you dc)
49 = (another) Epaulette
50 = Guild Emblem Item
51 = PET o.O (Anima lune probably)
54 = ?? (strange thing is having it freezen to this value before login don't let you login o.O, i think some kind of premium item)
56 = X-Gen card
58 = "the item can be used only when in a Mission Battlefield"
59 = Legacy Weapon
80 = CRASH!?! o.O
81 = crash too
82 = still crash...
So, that's what i know of it.
Thanks a lot for this tip, perfectoclan!
I'm still trying to find the way to dupe other type of item... I think of finding a way to put the item to dupe in bracelet slot WITHOUT changing it to an accessory, then use another item to dupe the accessory equiped -> dupe the desired item. This was my THEORY, but I din't manage to get it... maybe I'm wrong, or maybe those above will help someone to discover it