Keep in mind that when Team Flare Hyper Gear is removed from a Pokemon it is immediately sent to its owner's discard pile, as stated on the card. You can't use Tool Retriever to put your opponent's Head Ringer into your hand and play it on them. That would be silly. The same would apply for an effect that directly moves tools, like Mr. Mime PRC's Trick. You could target a Head Ringer, but instead of moving it from one Pokemon to another it would just get discarded because it was detached.