Okay, this is going to be a walkthrough to replace the in-game Coquette with this model here. I've figured it out and it works, but the poster that posted this mod did not make it easy so it's a lot to follow. I'll try to write it in a way folks can understand, but you're going to have to do a bit of work here.

First, download this file, then extract it to a folder somewhere.

Once that's done you should end up with a "update" sub-folder, follow it down the tree (update -> x64 -> dlcpacks -> c7) and then you should end up with a "dlc.rpf" file. Once you get here then you need to open up OpenIV and go to File menu -> Open archive... and browse to where c7.rpf is that you extracted, and open it in OpenIV.

Once you get there, you will see that the dlc.rpf has a lot of nested folders under it.

Inside of dlc.rpf you need to go to:
dlc.rpf -> x64 -> vehicles.rpf
Inside of this, there should be 3 files, "c7.yft", "c7_hi.yft", and "c7.ytd".

You need to extract these to a folder on your hard drive. Then rename them like this:
c7.yft -> coquette.yft
c7_hi.yft -> coquette_hi.yft
c7.ytd -> coquette.ytd

Once you have these files, then you need to go to the main GTAV game files and browse to this location:
Grand Theft Auto V -> x64e.rpf -> levels -> gta5 -> vehicles.rpf
Inside of here should be the original coquette.yft, coquette_hi.yft, and coquette.ytd. Just drag-drop in and replace the originals.

Then for the mods.

Inside of the dlc.rpf from this download, you should browse to:
dlc.rpf -> x64 -> vehiclemods
In this folder you should find the file "c7_mods.rpf". Just extract this to your hard drive, and rename it to "coquette_mods.rpf"
Then in the core GTAV files browse to:
Grand Theft Auto V -> x64i.rpf -> levels -> gta5 -> vehiclemods
In here, drag in and replace the original coquette_mods.rpf with the one you just renamed.

That should be it, good to go. File is beautiful and I love it.