Some changes going on here, mainly to the SB, but there's a one-card difference to the main as well.
-1 Unflinching Courage MB
+1 Dromoka's Command MB
-1 Suppression Field SB
+1 Pithing Needle SB
-1 Relic of Progenitus SB
+1 Rest in Peace SB
-2 Nature's Claim SB
+2 Natural State SB
There's a lot of one-for-one switches here, so I'm going to go through the SB first. Instead of 2x Suppression Field, I now have a 1-1 split between this and Pithing Needle. The same is true of Relic of Progenitus and Rest in Peace. I've decided on the split because there's definitely situations where one is better than the other in both pairs, but most of the time, they will both accomplish the task. I'd rather have a variety of solutions than go all-in on one.
Natural State is replacing Nature's Claim completely, as the 4 life hurdle is often too large of a burden for my deck to handle. I find myself avoiding casting Nature's Claim until it's absolutely unavoidable so that I don't have to deal with that extra 4 life. So, I'm losing the ability to hit Worship, and a couple of other things, but gaining a lot of castability.
The Dromoka's Command - Unflinching Courage switch is a little harder to explain. One of my largest issues with Unflinching Courage is that it is totally dead in my opening hand. It represents the absolute high-end of my deck, and I often side this card out in matchups where I need to be just a little bit faster, which account for a large number of my game 1 losses. I'm considering making room for Unflinching Courage in the sideboard, but my 75 is a very tight list right now, so this will potentially be a slow process. I'm bringing in Dromoka's Command as it's replacement for a number of reasons. Dromoka's Command helps to give me a lot of the same late-game action that Unflinching Courage does, but without sacrificing early-game flexibility. The fight mode on DC can, in a pinch, do an impersonation of either trample or lifelink. A +1/+1 counter is always a nice bonus, and essentially countering any non-Skullcrack burn spell can help out a lot against decks I otherwise don't have a good game 1 against. In short, I'm in love with Dromoka's Command, and we'll be eloping shortly. But in the meantime, it's back in the main. (This might mean that I go down to 3 Path to Exile in the main. 5 removal spells may be a bit much. We'll see!)