[2021] Im can't change Weapon costume! I add 3 but it dosent allow me the change is it a bug ?

Weapon skins and weapon costumes are 2 different things. What you bought is probably an appearance. A costume designer NPC will let you access those. Either that or you still have the unused costume items in the consumables section of your inventory. Or in your mailbox

Either that, or you bought for the wrong class. Mage and priest use different weapons and can't share weapon costumes