How to apply if condition to change values inside a function

Hi, I am writing a code for finding user position from the given satellite ephemeris and pseudoranges

I have calcuated satellite position perfectly at every epoch and now want to calculate user position using least square algorithm.

Now when I am using least square algorithm I want the satellite position to remain the same at first 5 epochs. after the 5th epoch I want to vary the 6 keplerian elements slightly and find user position based on the altered position...

Is it possible to put an IF condition where it changes the elements inside another function?