In all criminal cases, counsel for the defendant and for the government shall submit jury instructions to the court prior to the commencement of a jury trial, or earlier if ordered by the court. When it is necessary for counsel for the defendant to submit one or more jury instructions on an ex parte basis, those instructions must be disclosed to the government no later than the charge conference or when specified by the court. Subject to court approval, counsel may amend or supplement jury instructions after commencement of trial.