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Here's a different way of wording the ability that might help: All Heroes in play cannot be targeted by abilities on opponent's Heroes or by abilities on enhancement's used by opponent's Heroes.The most common application of this is that it stops opponent's Heroes from banding to other Heroes in play. It would also stop territory exchanges and placed enhancements that are placed on Heroes if the placed enhancement is used by one of opponent's Heroes.
I'm not 100% certain, but I think it would go through because modifiers target (modify) abilities, not cards, (similar to negate).