They usually are interchangeable but I think they can also have slightly different meanings. For example, "The Supreme Court functions as the guardian of the constitution" implies that the Supreme Court fulfils its purpose, the function it was designed for. "The Supreme Court operates as the guardian of the constitution" implies that its decisions have that effect, but not necessarily that it was designed for that purpose.

I would say конечно Here are a couple of examples: “The computer is functioning and operating well” “I can’t operate or function as a human when I don’t sleep enough!”