They could certainly talk about what the next administration would do.
NOPE.
lol Of course they could.
§953. Private correspondence with foreign governments
Any citizen of the United States, wherever he may be, who, without authority of the United States, directly or indirectly commences or carries on any correspondence or intercourse with any foreign government or any officer or agent thereof, with intent to influence the measures or conduct of any foreign government or of any officer or agent thereof, in relation to any disputes or controversies with the United States, or to defeat the measures of the United States, shall be fined under this title or imprisoned not more than three years, or both.
Flynn told the Russian ambassador to calm down, that the sanctions would be lifted once Trump got into office. That's nearly word for word, what a private citizen can't do.