Red Dead Redemption Outfit help *spoilers*?

I need to get the US Marshal outfit and the Bureau outfit. I know how to get them but can i get them for John to wear because you have to beat "The Last Enemy That Shall Be Destroyed." and isn't it to later for john to wear it then? Same thing with the Bureau Outfit you have to get 100% to unlock it but john will be gone by then. Am I missing something on how to continue playing as john or carry over data or are these outfits only obtainable for Jack Marston?