League of Legends (LoL) Question: Zed runes vs different mid laners?

Actually changing runes does not help you so much in game. It all depends on changing on gameplay and items you purchased from the shop. You should be fixed 1/2 rune pages for Zed and then later on in game, depends on which champion you are against, try to build up your item. If you face against an AD champion, then try to build armor and armor penetration, If you against a mage or sorcerer, magic resistant would be a good idea.

Actually, changing your runes can impact whether you get first blood or first death. Building items against a champion in every game, early game, is pretty much impossible unless you back every 2 minutes. Against AP champions, go the sorcery tree for secondary, Nullifying Orb for that sweet shield and Scorch for the extra damage. For the last three, I like to always go Attack Speed and then Damage, then mr or armor against that champion.