This came up in a recent game... I had Magic Charms placed on my magician and my opponent attacked me. I blocked, he did something to win the battle, and I was going to have to surrender a soul. So I announced that I was using Magic Charms to capture his hero. He then announced that he was playing Destruction on my Magic Charms.
I thought that for "Discard this card to..." artifacts like Magic Charms, Unholy Writ, Darius' Decree, etc., once it has been "used" (i.e., once I stated my intent to use it), you can't DON it, because the ability completes and the artifact is in the discard pile. Ruling?
Magic Charms - "Protect your Magicians from capture and conversion. You may discard this card from your Magician during battle to capture up to two Heroes."