"He who marches out of step hears another drum." ~ Ken Kesey
You could with a hardener but it still won't last very long. Water resistant diazo is the way to go.
I'm fixing to go down this road myself and planned on adding diazo to our Aquasol HV. It has very good water resistance already and diazo + hardener when needed sounds promising. Almost all of Murakami's photopolymers are rated for discharge- it sounds like photopolymers are a no-go for discharge from other brands but anyone have actual experience with Murakami's and these inks?Maybe try adding diazo if you are hell bent on staying with one emulsion. This will change expo values, give it a shelf life once sensitized and give it a little more latitude in addition to adding water resistance. Myself, I'm not at all opposed to having two emulsions for the different inks as you can choose different colors and have a fool-proof visual of which screens are for which seeing as the coating methods and overall processes are going to be different for each. Most suppliers and mfg's are overly generous with emulsion samples it seems, we still have quite a few qt.'s that I never even asked to trial.
I have use chromablue coated 2/2 and post harened in the sun for a couple hour and been able to print 100 2 color fronts and backs ganged on the same 2 screens without a problem.