There you go.
Open Forge.lua and search for the following function
can_fusion_item
Then in this function search for this code:
local ItemID_Waiguan = GetItemID ( Item_Waiguan )
below of this theres that:
if ItemID_Waiguan <= 4999 or ItemID_Waiguan >= xxxx then
Change the "xxxx" to the limit of apparel ids you want to