Look, i know there are probably a million threads with this general topic, but just hear me out ...

Nobody CLEARLY tells you how to get it in the file...

Theyre all just like , ya put it here ... then you spend 2 hours tryin to find it and finally give up ....

So... anyone care to make a step by step guide : How to get a custom PNG skin to the Police model ingame ? Please....?

Well I am not sure. I would just go to a website that has skins and download it. And to get skins in game you will need to download Spark IV, open it, click browse, scroll down to models>cd images> vehicles.img, one click the car you want(it will say wft, wtd and click on each for each file) click import on top bar, go to where you downloaded skins, click either the wtd file or wft(which ever one you selected) and it will import it. then once you did it for both, click rebuild THEN save.