Flappu

1) Unfortunately I'm not sure about that, or if you even can force certain wheels.  It might be do-able in the vehicles.meta, but I'm not positive.
 
2)  You need to add a new carvariations line for policeold1 and policeold2, especially to fix the headlights and make them normal.  In the topic I'm linking below, I provide a carvariations line you can use.  Open OpenIV and navigate to mpchristmas2 and grab the carvariations from there.  Just copy and paste the carvariation line from my topic twice in the mpchristmas2 carvariations, and change the name appropriately for both of the new carvariation lines.  That's all you need to do aside from changing the spawn colors hex.
 
Check the bottom of the post -
 

Thanks for that amazing explanation, worked well for me aswell. One problem though, how do I change the colour hex?
Nevermind, I got it working. Thanks again!