just change the path of the DISBTN(in the import manager) like this
Interface Icon - ReplaceableTextures\CommandButtons\BTNItem
DISBTN - ReplaceableTextures\CommandButtonsDisabled\DISBTNItem
anyway, you always need to use those
ReplaceableTextures\CommandButtons\ and ReplaceableTextures\CommandButtonsDisabled\ for the icon paths or else it won't work
and don't ever try changing the path in the Advanced - Game Interface because that would cause bugs for the in-game icons...