SimBiology

Hi, In simbiology design app, is there a way to define a species like a step fucntion so that it increases to a constant after a specific time point? I tried to use 'events' to trigger a species increase after a time piont, but the species is not a constant and changed during reactions. I also tried to 'dose', which behaved same as 'event' triggered species increase. There are examples of codes where a user defined function was used in conjunction with repeated assignments. However, in design app, code can't seem to be edited. Thank you very much! -Ji