By "you", you probably mean ToddRivers. 😃
What you need to do is either make a duplicate Material of your skeleton, using the shader you want, as an asset in Project View or at runtime using new Material(originalMaterial). Then set its shader and material properties to the one you want.
Then do something like this:
void ApplySpecialMaterial (Material myModifiedMaterial) {
SkeletonAnimation skeletonAnimation = GetComponent<SkeletonAnimation>();
Slot myWeaponSlot = skeletonAnimation.skeleton.FindSlot("my weapon slot");
skeletonAnimation.CustomSlotMaterials.Add(myWeaponSlot, myModifiedMaterial);
}
This causes any attachments in myWeaponSlot to be rendered using myModifiedMaterial.
