Fair enough to keep
Dissipate, exiling spells could be usefull sometimes. I find that usually spending less mana to counter a dangerous spell is more worth it, but of course that depends on your more frequent match-ups!
I play with black mana decks the most of my time, and I can tell you this: life is a resource, don't be afraid to use it. Especially in cEDH, you are going to face many combos that can kill you even if you got a lot of life. If you can pay life to get card advantage, board advantage or tutors, just go for it. Most of the times, the amount of life you paid to get these advantages is less relevant then the threat of the opponent.
About the cards you mentioned:
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Razorlash Transmogrant is a recurrent card draw with my Wilhelt. Against not-monocolored decks, I can pay 2 black mana each turn to get a card and a decayed zombie. Since against monocolor is quite weaker, I understand if you don't wanna add it to your list! But you could use it to easily untap your Grimgrin each turn most of the times, if you couldn't manage to play
Gravecrawler yet.
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Leyline of Anticipation is sooo great. In a creature-based deck as ours, having the chance to cast them at the end of the opponent's turn (or actually when you need it the most) is life changing. In cEDH, having flash in all of your cards means you can play your combo pieces at the optimal timing, reducing the risks of removals and counters and gaining a heck of a lot of control in the game. I play it in almost every blue deck I have, and often I'm happy to play it even if I have to cast it paying all her 4 manas.
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Cleaver Skaab is not optimal. I keep him because he can easily make useless most of the single-target removals of my opponents by activating his ability when the removal spell declared the target. The problem is he usually doesn't survive the turn I play him.
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Compelling Deterrence is in my deck because I don't have yet
Cyclonic Rift. Just keep going with that one
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Change of Plans can defend some of my combo pieces while making me draw cards, feeding my graveyard and powering up my creatures. Not bad for an instant, but of course it requires some mana if you wanna protect more creatures.
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Military Intelligence is going out soon. It was an ok card in casual commander, but in cEDH it's just weak. I'm replacing it with
Necropotence! I hate having to
exile the cards I discard, but drawing that amount of cards at will it's just overwhelming.