"Individuals and interactions over processes and tools" ...people are more important than any process ..and considering them "resources" is not valuing people enough.
What i said has nothing to do with team roles
But they are not to be taken away from the team during a sprint! There is absolutely no recommendation to change the teams between sprints for the sake of changing either.
The interchangeable part (although I have never heard it called that) is more that knowledge should be spread, so you don't end up with domain experts that end up "owning" part of the code.