I am currently DMing my first campaign in D&D 5E and had opened up the use of feats to the players. I really like how feats give each of the players another way to differentiate from one another. That got me thinking that this would be an interesting thing to add to monsters/enemies and NPCs. But would enemies with feats change encounter balance/CR?
Let me give you a concrete example: If I have a party of 4 Level 1 adventurers squaring off against 4 Thugs (CR 1/2), the encounter would be classified as "Deadly". Now what if I had the same encounter but each Thug had the "Dual Wielder" feat which gives +1 AC and the ability to dual wield maces. Would the encounter still be classified as "Deadly" or does it cross over into "Overwhelming"?
If I were to give feats to monsters/enemies, what would be a good way to go about incorporating that into the encounter difficulty mechanic?