Yes. The dead load associated with a typical plasterboard lining is insignificant when compared with the design imposed (live) loads for loadbearing floors, it is therefore not considered a detrimental factor in relation to the fire resistance of the floor. Provided the base tested system is maintained and no other modifications are made that could effect performance, the addition of a further plasterboard lining will serve to increase the fire resistance and remain well within the structural capacity of the floor.