Colonel [Col]
Lieutenant Colonel [LtCol]
Major [Maj]
Captain [Cpt]
Lieutenant [Lt]
Ensign [Ens]
Serjeant Major [SjtMaj]
Colour Serjeant [CSJt]
Serjeant [Sjt]
Corporal [Cpl]
Lance Corporal [LCpl]
Veteran [Vet]
Regular [Rgl]
Private [Pte]
Recruit [Rct]
I didn't touch the lowest ranks save for changing Pvt to Pte and Cadet for recruit, a tad more accurate. And I popped in Colour Serjeant. And at this time (early 1800's) there was still ensign instead of second lieutenant. If you want another NCO rank I'd go with Lance Serjeant. And perhaps replace veteran with Guardsman, Kingsman or Fusilier. Just some possible changes