Is it possible to be demoted from a second lieutenant to command sergeant major?

No, and any Command Sergeant Major would probably knock you upside the head for considering it a demotion (or even considering it at all). Second Lieutenant is an entry level Commissioned Officer rank. Command Sergeant Major is a very senior enlisted rank... even though a Second Lieutenant may technically outrank a Command Sergeant Major by being a Commissioned Officer, you will never see a Second Lieutenant trying to give orders to a CSM. A Second Lieutenant does not have the time in service or experience to be anywhere near ready to take on a CSM's duties. In fact, a Second Lieutenant is not even experienced enough to take on an ordinary Sergeant's duties (save perhaps for some who had served in the enlisted ranks prior to getting their commission).