Counterfactual simulation with interest rate to be 0

I am trying to do a counterfactual simulation with simult_(). What I am trying to do is set one endogenous variable (nominal interest rate) i_t to be constant from period T onward (i_(T+t)=i_T for all t>0). Is there a way to achieve this by give a specific pattern of the monetary policy shock? Or are there any other ways to do this?