I've been considering doing that, but for now, I'm just focusing on making retextures that go like (State Trooper, then a city police department within that respected state.) Considering I'm trying to cover all 50 States, and I don't want to get burned out before completing that goal.
Oh, no. The only thing that should change is the ytd files. To my knowledge (It's been a month since I uploaded this) there shouldn't be any ydd files in the pack and by chance, if there is one then nothing should change if you have eup 9.4 and above. I can't say the same for the eup on lcpdfr website considering that one is an older version.
I changed the majority of SAHP textures (no models were included considering I don't own the models themselves) in this pack and included a few other clothing textures, such as the pullover and baseball cap, for more variation. But if you're asking for one where the presetoutfit isn't changed, I could consider doing something like that in the future.
After dropping files in Open IV, the game might crash without the Rage thing popping up (I assume a gta thing, I'm not sure). If this is so then just reload into the game and it should work but I'll look into this later tonight.
For the vehicles (Textures at least), you can find where the "Hidden contents" are, but you can also just google Charlottle lspdfr or something similar to that and find it that way.