The easiest way is to use the simult_-function to simulate a combination of surprise and news shocks. A four period deterministic shock is the same as a simultaneous surprise shocks coupled with a 1, 2, and 3 period anticipated news shock. See https://github.com/JohannesPfeifer/DSGE_mod/blob/master/RBC_news_shock_model/RBC_news_shock_model.mod on how to do something like this.
What puzzles me in your mod file is that z is a shock entering an AR(1) process. That way, the four period shock will accumulate effects via shocks in every single one of the 4 periods. Is that desired?