This unlock pack contains a savegame with everything unlocked:

Unlocks all cars, all tracks, all regions, all rewards, rank 30

And one savegame which just unlocks all cars

Install: Copy the savepool.xml of your choice to 

"Steam Directory\UserData\UserID\202310\local\Ridge Racer Unbounded\Autosave.bin\"

XP: "User Profile\Local Settings\Application Data\SKIDROW\202310\Data\Ridge Racer Unbounded\Autosave.bin\"

Don't forget to make a backup of your current savegame!

Cheers, ADHDerby