Answering the initial question before everything went off track
There is no police rule to my understanding that prevents you from taking multiple firearms on patrol, for example having an SMG on your vest etc. As I have done it many a times.
Saying this, don't go insane taking 7 SMGs on patrol with you, that's just ridiculous. If you believe you would do a better job carrying a more effective firearm for situations you're in then go ahead.
I hope this answered your actual question before stuff started going completely against what you actually asked.