Unless you cut wires and then put quick disconnects on them, thereby negating the need for future cutting, you will need to cut wires to make the install.
I realize that different jurisdictions have different laws about who can run what, where, and why, but...the first question that springs to my mind is that if you have a legitimate need for such flashers, how come you don't have your agency's fleet shop advise you on such matters, and/or do the job for you?