Gunfights in Watch Dogs after beating the game
Solution 1:
I too would like to replay the Hideout mission again! Better yet, more new, bigger, harder hideouts.
Two ways that I've found to face off with the cops indefinitely and without lowering my vigilante status;
Engage the cops in an "Online Free Roam" game (either join or setup a session). Remember though, once you endt the online game, the cops will still be searching for you. Killing cops or citizens at this point will lower your reputation. At this point either lose them or end the game as in point 2.
In your single's game, just start a battle with the cops. The trick is, when you are finish with the battle, make sure that you either kill yourself or get kill by the cops. The game will reload your last save. Your stats will NOT be affected.
Do keep in mine that the game has a tendency to cheat by inserting cops behind you.
Solution 2:
It might be a bit late to respond to this, but I'll leave it anyway. I'm like you, I like to keep my reputation a bit high but like to engage in a fair bit of the ol' ultra violence now and again. What I found worked best was to do one of the infinitely generated crimes and wait until I ran into a guy who could call reinforcements, their icon is usually a star with two curved lines next to it, like this.
((*))
Chase them for a while, don't lose them or take them out, and wait for them to call in some backup. When they do, anywhere from two to five cars can show up with bad guys to shoot it out with. I'd recommend bringing a lot of 'jam comms' craftables with you though, they have a tendency to shoot at you while you chase them and civvies tend to call the cops right away when that happens.