simulation with uncertainty of THETA

Dear all, When do the simulation, if I have all of the parameter information from literature and internal data, I will fix the PKPD parameter and add about 30% for PK and 40% for PD as IIV. But my question is do we need to think about the CV% of THETA, since we fixed it, we could not add it in one run. if it is necessary, for instance, we will add 20% of CV to one mean THETA, how to do it, or does PsN can implement this issue? Best Ying