Hi. Yeah its extremely configurable and can be tailored for an RP server.
As far as limiting it to cops can only take missions, that would require you to change some of the code. You can check out the “…Optin” settings in the missions.lua where you can have it that only players that opt-in to the mission can take it, and then from there in the client.lua look for where those values are used as well as mrpoptin/mrpoptout decor values. Basically when an …Optin value is used, the decor values determine who is in the mission or not. I would imagine that you would need to check for player police skins as well in your case.
I actually have a massive update coming out in the next few days, which I would wait for, it has a load more improvements.