I am 80% sure 3 is the max, but the wiser heads will correct me if I am wrong, shortly.
What I did want to mention early on is that you should move with caution if you try any experimentation. If you cause the system id to cycle, you will need new PRI enabler codes, and those are increasingly hard to come by now. If you lose your codes, code retrieval is also much harder now that the KRS is flirting with end of life status. There are a few gifted master techs that can work keycode magic outside of the KRS, but they are becoming ever fewer and farther between. Just a word of caution.