I think CatKnight has just said all I would have said about the subplot, but as regards to historical characters, here is one approach.
Take Winston Churchill. Historically he is the great defender of democracy, who (in effect) sacrificced an Empire for the freedom of Europe. A stalwart and principled man, stuck to his guns and all that. We all know that from what he did in WW2, but consider stressing just a couple of different aspects of his personality. A rigid imperialist, sponsor of some rather nasty paramilitary groups in the Irish war, a political turncoat (he was widely thought to be unreliable in the 1930s, having switched parties not once but twice) - not difficult to paint a very different Churchill by concentrating on different aspects. By doing that you can quite easily end up portraying historical characters in quite different roles, yet by keeping plausibility.
Take Winston Churchill. Historically he is the great defender of democracy, who (in effect) sacrificced an Empire for the freedom of Europe. A stalwart and principled man, stuck to his guns and all that. We all know that from what he did in WW2, but consider stressing just a couple of different aspects of his personality. A rigid imperialist, sponsor of some rather nasty paramilitary groups in the Irish war, a political turncoat (he was widely thought to be unreliable in the 1930s, having switched parties not once but twice) - not difficult to paint a very different Churchill by concentrating on different aspects. By doing that you can quite easily end up portraying historical characters in quite different roles, yet by keeping plausibility.