Multiplayer uses the Reach Engine so you'll likely have the same options for customization that you had there. Campaign will probably be different. It would take a fair amount of coding to let you have a whole armoury for use in the campaign, and it wouldn't make sense for you to be able to change, since unlike in Reach where you are Noble-6 and so how you customize your armour is how you would do it ingame, in Halo: CE you are the Master Chief and he has his armour the way you've already seen it.