If your playing as Man United you don't need to fiddle too much with custom tactics in my opinion, I find them to be near enough spot on. One thing I do change though is that I change Ronaldo's base position from RM to RW, make sure his work rate is assigned to low defence and I point his "attacking arrow" toward goal and not up the wing if you know what I mean. To compensate for this though I make sure one of my CM's is ultra defensive.
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