@Killroy Skins will not impact your MP experience, only you will see them.
To choose a skin, it’s done via the LOADOUT page when you’re on the MAP of a mission. Simply click “Change skin” until you see it.
(on a side note: that skins are tied to “sets”, so if you have clicked 4 times “change skin” to find the relevant skin you want to fly with, it will also have change 4 times the skins for all other aircraft in the TE, wathever their skin will show (in a campaign it’s different, a file dictate wich set is used for each squadron))