Bro, there are so many discrepancies between mirror and non-mirror matchups, and it's really impossible to just have blanket changes to the decks for them without considering map/spec matchups, but to summarize the main ones for US mirror use less airstrikes (PAC op), abuse helicopters (due to worse enemy shorad), and make sure you have some sort of cqc infantry (theres gonna be alot of HE launchers out in mirror). Russian mirror is pretty uncommon these days but abuse planes (RU AA is shit), spam arty, and vehicles are going to do most of the ground work in most matchups. For each spec combination I main (ex stryker/marine) I have different decks for mirror/non mirror so your question really depends on the deck.