If you want, I can explain how to inspect dlc.rpf contents with OpenIV, show typical setup.xml entries for a dlcpack, or outline safe modding practices. Which would you prefer?
The dlcpack, found at update/x64/dlcpacks/mpchristmas2017/dlc.rpf , contains the data for the Festive Surprise 2017 and The Doomsday Heist updates for Grand Theft Auto V. Update X64 Dlcpacks Mpchristmas2017 Dlc.rpf
For advanced modders, this DLC pack serves as an excellent template for creating persistent add-on vehicles because it loads early in the game’s startup sequence. If you want, I can explain how to inspect dlc