This is different. Someone who is supposed to be a commissioned officer in Confederate service should have a service record, and this man does.
John M. Granberry enlisted at Columbus GA on May 23, 1861 and was elected 2nd Lieutenant of Co. "B", 20th Georgia Regiment. He served throughout the war and was eventually promoted to 1st Lieutenant. I see nothing in his file (forty-one images) referring to staff service. That may be possible for the last weeks of the war, but I have reviewed staff appointments for the Alabama brigade led by Col. Bowles and have not seen this name.
At the time of the 1850 census John M. Granberry lived in Harris County GA. In 1855 he purchased land in Florida.
If there is a Louisiana connection, I don't find one. Peter and Louisa Grenbury lived in Ward 9 of New Orleans. Other than these two, no one by the name Granberry or anything close is reported on the 1860 census of Lousiana.