In a network, opening and closing of one valve will be very frequent and as a result of that in that particular region the temperature and Pressure will also change. Fo far I know, CAESAR considers f value (in the formula of Allowable Stress Range) as 1. Here in my case the number of cycles that I need to consider is more than 7000. Is there any way to select the f value manually? One option that I know is that I can calculate the Allowable stress range manually and that value can be given selection a non-standard material. Is there any other option to do the same?

You can input the value of "f" directly. The field is on the "allowable stress" dialog, right next to the "hot allowable".