@kyle4600 you can do it yourself by renaming the files under

Step 1
Download 'Easy Mod Folder' if you haven't already and install (there's a install tutorial on the page)
https://www.gta5-mods.com/tools/car-weapon-folder-for-replacer

Step 2 locate this location from the zip file you downloaded from this page - ford mustang nfs etc
'updata\x64\dlcpacks\mustang'

Step 3
Open 'Mustang' folder and extract 'dlc.rpf' to desktop

Step 4
Open 'OpenIV', enable 'Edit Mode' and locate (Through OpenIV)
'\mods\update\x64\dlcpacks\EMF\dlc.rpf\x64\vehicles.rpf\'

(This folder will be empty if you just installed 'EMF')

Step 5
Drag 'dlc.rpf' from your desktop to 'Vehicles.rpf' empty page

Step 6
Double click on 'dlc.rpf' and go to this location
'\mods\update\x64\dlcpacks\EMF\dlc.rpf\x64\vehicles.rpf\dlc.rpf\x64\'

Step 7
Double click on 'vehicles.rpf'

You should now see the files:
'mst.yft'
'mst.ytd'
'mst_hi.yft'

Drag these files to desktop

Step 8
Rename the files to whatever car you would like to replace.

For example, I chose:

'dominator.yft'
'dominator.ytd'
'dominator_hi.yft'

Step 9
Go back to 'OpenIV' and go to this location (Basically Step 4)

'\mods\update\x64\dlcpacks\EMF\dlc.rpf\x64\vehicles.rpf\'

Delete 'dlc.rpf' from the 'vehicles.rpf' folder.

Step 10
Your 'vehicles.rpf' folder should be empty again.
Drag and drop these files from your desktop to the 'vehicles.rpf' folder:

'dominator.yft'
'dominator.ytd'
'dominator_hi.yft'

This is the folder you place the files on the cars you'd like to replace in game, everything is explained through the 'Easy Mod Folder' link I posted on Step 1.

That's it, you're good to go!

Spawn in a 'Dominator' through a trainer or wait until you see a npc drive by.

Note: I noticed the roof is slightly transparent.. like a window tint, I know this isn't an issue if you use this mod as an addon which is what it's intended for. To be honest the camera angle does a good job hiding it but that depends on the colour you spray the car I guess.