Hello Melih Ozbagi,
If its for all material pertaining to one item category than OS21 will work.But at new bom creation it will set unchecked relevancy to cost in bom items.so it cant be set material wise except if it is bulk material. If this material is co-product and negative quantity set than this indicator have no effect of costing.
you need to set this up individually for materials.
Regards,