I just saw this fivem script that allows you to put a lightbar on any vehicle in game.

think simple trainer but with lightbars.

Here it is : https://forum.cfx.re/t/release-lightbar-menu-script-attatch-lightbars-to-any-vehicle-w-sirens/905786

I was wondering if there was a similar script for singleplayer, or a way to run fivem scripts in singleplayer.