Here is a link to the original Chalice Black thread.
http://www.themanadrain.com/forums/viewtopic.php?t=11664Now, let's see what changes you made.
-4 Chalice of the Void, +3 Null Rod, +1 Vampiric Tutor
First, the importance of Chalice of the Void from the other thread.
Null Rod versus Chalice: Null Rod doesn't stop burn, Plows, Duress, and Brainstorms. It forces Moxen in hand however, which dilutes Hymns.
Your big threats are Brainstorm against discard and sword and burn against your threats. COTV helps your deck more than Null Rods.
Second, Vampiric Tutor is not going to help you that much. Your deck is redundant enough that you will probably topdeck something good anyways. Demonic Consultation is the better of the two 1cc tutors.
-1 Lotus Petal, +1 Necropotence
Lotus Petal is there for the early game so you can cast your spells quicker. Necropotence is there for the longer game. It's usually there for the control matchup, but if you have COTV, then you shut down a lot of their options and can go for the quicker victory.
-3 Swamp, +3 Bloodstained Mire
The fetchlands are there to thin your deck. However, do you really want to thin your deck? With Sphere of Resistance and Nantuko Shade, topdecking lands isn't so bad.
-4 Mishra's Factory, +4 Withered Wretch
Again, with Sphere of Resistance, you don't mind a threat that can be played underneath it. Withered Wretch seems to be better suited in a more controlish deck because this deck wants to be aggressive. I would leave then in the sideboard, and when they side in, use a different slot instead of a land slot to come into.