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Umm, I know that in the Deathly Hallows, it is said that snitches can carry messages on them when Rufus Scrimgeour ais trying to get something out of Harry in the beginning of the book.
I'll be perusing through Deathly Hallows this evening looking for this. It is certainly possible it has slipped my mind.
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As for Dumbledore bewitching it to hold something...I'm not sure. I would think that either the snitches naturally can and open once the person touches it unless the sender bewitches it to open at a certain point...e.g. "I open at the close."
The reason I think bewitchment is more plausible is due to the convenience of it all should the nature of a Snitch be that it can hold messages/objects. Why mention this at the end of the series making it seem like a desperate add-on? Dumbledore could easily bewitch the magical ball, providing the message-holding ability of the Snitch while preserving JK Rowling's writing quality.
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Or the witch/wizard has to bewitch it to hold something every time.
I'm not sure which one is true if either is at all, maybe there is some other possibility that we're missing. The part that makes it a hard call is that Dumbledore was the sender because when he sends, then we don't know if any wizard can bewitch or just someone like Dumbledore...what do you think?
I must admit that I am lost with the last part of your post.