Yes, the President can issue a pardon to a person convicted at court-martial. His unfettered right to do so is spelled out in the U. S. Constitution.
Most recently the President did that in the case of United States v. Behenna.
Yes, the President can give clemency through a sentence commutation, as was done in the case of Chelsea Manning.
So, there is a past history of presidential clemency and pardons.
President Obama pardoned a Soldier convicted at GCM, at Fort Benning, GA, of 23 bad check offenses and use of cocaine; and an officer convictedof Art. 133, from Fort Benning, GA. Each president has granted relief for several military personnel. For example, see G. W. Bush here--https://www.justice.gov/pardon/gwbush-pardons.
You can see all of the statistics going back to President Nixon at this website.
And overall statistics are here.
No there is no method to expunge the record of a court-martial conviction. And, a pardon won't do that either.
No. Expungement is a judicial remedy that is rarely granted by the court and cannot be granted within the Department of Justice or by the President. Please also be aware that if you were to be granted a presidential pardon, the pardoned offense would not be removed from your criminal record. Instead, both the federal conviction as well as the pardon would both appear on your record. However, a pardon will facilitate removal of legal disabilities imposed because of the conviction, and should lessen to some extent the stigma arising from the conviction. In addition, a pardon may be helpful in obtaining licenses, bonding, or employment. If you are seeking expungement of a federal offense, please contact the court of conviction. If you are seeking expungement of a state conviction, which the Office of the Pardon Attorney also does not have authority to handle, states have different procedures for “expunging” a conviction or “clearing” the record of a criminal conviction. To pursue relief of a state conviction, you should contact the Governor or state Attorney General in the state in which you were convicted for assistance.
As a general rule, despite recent clemency actions, a person must wait for five years after completion of all punishment and collateral requirements before a petition will be considered. So,
A military prisoner is released at the MRD (minimum release date or earlier); they will be on parole or MSRP until their FTD (full term date). The five years begins on the FTD.
The current clemency discussions surrounding President Trump are an anomaly in the pardon process. You should not expect to be treated similarly to those clemency actions of President Trump.
Call or email if you want to discuss submitting a clemency petition to the President. Keep in mind the package needed will be extensive and the background checks usually performed are very thorough and detailed (I analogize that to seeking a TS clearance with SCI access--on steroids).