Create / Edit Car mods... But how?

Hey guys,
I would like to ask here how I can actually edit a GTA V Car mod. So, for example put a lightbar on it.
I am familiar with modeling and can program. Unfortunately, I have found nothing useful online and I would like to continue my education here!

Best regards, MaLeTut

ZModeler: https://www.zmodeler3.com/
LSPDFR Website (many tutorials): http://lcpdfr.com

I highly doubt you did not see anything: http://bfy.tw/HoEZ