Color Schemes of Norwegian F-5 and F-104 Fighters

For The GTAV F-5E
Once installed with their instructions, open the dlc.rpf with OpenIV
Follow this path to the file to overwrite:
...\GTAV\mods\update\x64\dlcpacks\f5adv\dlc.rpf\x64\levels\gta5\vehicles\vehicles.rpf\f5adv.ytd
If you wish to retain the original USAF livery, while in OpenIV, extract the file f5adv.ytd. I typically extract the original .ytd to the same folder as the dlc.rpf and rename it to origf5adv.ytd.
When ready to overwrite with the Norwegian F-5 livery, toggle "Edit mode", top right button, and drag f5_sign_Norway.dds from the extracted zip file and drop here:
...\GTAV\mods\update\x64\dlcpacks\f5adv\dlc.rpf\x64\levels\gta5\vehicles\vehicles.rpf\f5adv.ytd, then rename to f5adv_sign_1 or the next available sign number
You might be able to add the new liveries to f5adv.ytd, but when I tried that, it seemed to surpass the size limit for a .ytd file.
Just to confirm the livery, I'd click on the f5adv.yft or f5adv_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 f5adv with the trainer of your choice.

For SkylineGTRFreak's Lockheed F-104C Starfighter
Once installed with their instructions, open the dlc.rpf with OpenIV
Follow this path to the file to overwrite:
...\GTAV\mods\update\x64\dlcpacks\f104c\dlc.rpf\x64\levels\gta5\vehicles\vehicles.rpf\f104c.ytd
If you wish to retain the original Bare Metal USAF livery, while in OpenIV, extract the file f104c.ytd. I typically extract the original .ytd to the same folder as the dlc.rpf and rename it to origf104c.ytd.
When ready to overwrite with one of the Norwegian F-104 liveries, toggle "Edit mode", top right button, and drag F-104CNorwayGreen.dds or F-104CNorway from the extracted zip file and drop here:
...GTAV/mods/update/x64/dlcpacks/flyingbox/dlc.rpf/x64/levels/gta5/vehicles.rpf/f104c.ytd, then rename to f104c_sign_1
You might be able to add the new liveries to f104c2.ytd, but when I tried that, it seemed to surpass the size limit for a .ytd file. You could replace the liveries in the f104c2.ytd file with the enclosed liveries, following the same process, but for f104c_sign_6, for example instead of f104c_sign_1
Just to confirm the livery, I'd click on the f104c.yft or f104c_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 f104c with the trainer of your choice.