If you want different .prf files to be generated , then try breaking the simulation period in smaller time periods . you can use the Hot Start functionality to set up the initial conditions for next simulation. For example,If I have to perform a simulation for 2 days period, then I generally divide it into 2 simulation periods and use the conditions from 1st day simulation and set in the hot start for next day simulation.
Hope I'm clear. let me know if you require further information. You can use Mike Urban manual and read about Hot Start functionality.