[Help] Manipulate texture alpha through script

Hello everyone!
I’m having a nasty little inconvenience I hope someone can help me solve.

I almost finished successfully porting a singleplayer mod into my own server (a nice custom car). Everything, from scripts (written by myself) to custom sounds is working flawlessly. There is still one thing that is driving me mad. It seems the car’s main texture has an alpha channel that adds a nice overlay to it. Problem is, the alpha opacity is random any single time I spawn the car. So my question is:

How can I make a script to control the alpha opacity of the main texture, and set it to a default value, and then ONLY IF CERTAIN CONDITIONS ARE MET the opacity is randomized? I’ve looked in the whole graphics section of the natives, but couldn’t find anything useful

Thank you all!