>>All defendants have the right to make requests for such things...through filing motions in court.Snowden is asking (strictly speaking, his father is asking on his behalf) for extrajudicial guarantees that are not mentioned in the constitution or available to normal defendants.

Extrajudicial guarantees are absolutely meaningless in a judicial court. Simply because Snowden and the justice department make a deal to obtain his extradition doesn't mean that the court has to accept the deal. The court will rule based on the particulars of the case not on what is convenient for the government.