DISPLAY ONLY attributes are useless to add, because they're actually implemented in either the weapon class itself or as part of another attribute. The former is why the Bazaar Bargain is a tf_weapon_sniperrifle_decap instead of a tf_weapon_sniperrifle.
With the Machina, it's likely that "sniper penetrate players when charged" (attribute 308 ) also implements the tracer rounds.
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Not currently working on SourceMod plugin development.