Furthermore

For The GTAV Mirage 5, "Iron Eagle" Bilya "MiG-23"

Once installed with their instructions, open the dlc.rpf with OpenIV.

Follow this path to the file to overwrite:

...\GTAV\mods\update\x64\dlcpacks\mirage5\dlc.rpf\x64\levels\gta5\vehicles\mirage5vehicles.rpf\mirage5.ytd

If you wish to retain the original livery, while in OpenIV, extract the file mirage5.ytd. I typically extract the original .ytd to the same folder as the dlc.rpf and rename it to orig_mirage5.ytd.

Toggle "Edit mode", top right button, and drag mirage5.ytd from the extracted zip file and drop here:

...\GTAV\mods\update\x64\dlcpacks\mirage5\dlc.rpf\x64\levels\gta5\vehicles\mirage5vehicles.rpf\mirage5.ytd

Just to confirm the livery, I'd click on the mirage5.yft or mirage5_hi.yft file to open the OpenIV Model Viewer to see what the model will look like with the new livery.

Once satisfied, close the model viewer and run GTAV and spawn mirage5 with the trainer of your choice.