Obvious course of action would be to build it OOB as the Titanic, BUT... I'm really leaning toward building it as the third Olympic sister ship, HMHS Britannic, as she appeared in service as a hospital ship in 1916. This would require a few modifcations to the base kit- the addition of more lifeboats and different davits, mostly, but I think it would look very nice with a bit of light weathering. Yes, the Olympic was 2' wider than Titanic, but I don't think that would be very noticable in 1:1200 scale!
I was also toying with finishing the hull in 'dazzle' paint, to depict the Olympic as she appeared while in service as a troop transport. That conversion might be a little bit easier, but dazzle paint on a hull this size may be a bit beyond my skill set at this time.