If I remember correctly, there were three different Buckys, with one of them changing the name altogether and becoming Nomad.
If anything, Sam being Cap may play out in one of their alternate universes, just like how Moralez is Spiderman.
Interesting here to note how no-one has complained about Nick Fury. But it's okay for him to have the race change, no? Or even notice how no-one has complained that before CA: The First Avenger came out, Captain America was
DEAD. Shot and killed by his wife. But throw in a race change - and in Thor's case, a gender change - and everyone gets up in arms.
Side note about Rogers being dead; they could have really complicated things if the shooter had yelled out "Justice is Served!" - bringing the entire
Scourge story back from the dead (pun intended).
BL.