for this purpose you will need sanny builder to edit main.scm only bw mission builder and sanny builder can edit main scm for gta when you open it it will have too many codes but you will need to find the exact code of the Madd Dogg's Cribb?
and if you want to add Elegant to this place then use cleo for this script it will easily add the vehicle you want

or if you want to delete the car then find the exact coordinate of that area then deleted it simply