You should set "costume = true" value in your item info for equips that you want to show in costume tab.
Example:
[2206] = {
unidentifiedDisplayName = "Hat",
unidentifiedResourceName = "ĸ",
unidentifiedDescriptionName = { "Unknown Item, can be identified by using a ^6666CCMagnifier^000000." },
identifiedDisplayName = "Wedding Veil",
identifiedResourceName = "�����",
identifiedDescriptionName = {
"A transparent veil worn by brides on the day of their wedding.",
"Mdef +5",
"Class:^6666CC Headgear^000000",
"Defense:^0000FF 0^000000",
"Position:^6666CC Upper^000000",
"Weight:^009900 10^000000",
"Jobs:^6666CC Female Only",
"All jobs^000000"
},
slotCount = 0,
ClassNum = 44,
costume = true
},