Because of the protonation of acid, it must depend on the solution pH! at basic solutions, the acid may behave like an anionic surfactant and have a synergistic effect on micelles of the cationic surfactant. The aggregation number depends on the concentration and ratio of both components. a quick review of the literature will show that depending on the concentrations of both surfactants you may have micellar phase changes from spherical to cylindrical or worm-like micelles or vice versa! the non-spherical micelles have higher aggregation numbers! Nevertheless, the best way to make sure is to investigate it yourself as surfactants' physico-chemical behaviour is so variable from system to system!