As far as I recall, item rarities can't be done due to the way they're programmed. However, I would love some kind of label or tool tip at least so we can know what month/year and/or event or circumstance an item was released without having to search the archive (would be especially useful for items that were from the store as those currently don't have any indicator when looking at archive, adding/removing in trades, or viewing trades).
-fireflii