If the replacer vehicle doesn't spawns but the vanilla one does, the problem is that the game finds the vanilla vehicle as the most recent version. That can be caused because of the following:
1.- The EMF folder is not being read by the game when you start it. Make 100% sure that you've installed it correctly, following every step, without mistakes of any kind.
2.- The LSSD Charger vehicle that you've mentioned does not work or the files of the vehicle installed are corrupt, which makes the game unable to load it and instead spawns the most recent "police2" files found.
3.- If it still doesn't work and you've verified that's not a mistake with its installation, you still have the chance to try another installation method, similar to EMF. If you want to try this method, I'd suggest you to do a test with the tutorial available first. If you got the tutorial example working, then you should be able to create your own Add-Ons, because you'd have made one!