The .yft files will go here:
mods\update\x64\dlcpacks\mpg9ec\dlc.rpf\x64\
levels\gta5\vehicles\mpg9ec.rpf

You'll have to use a trainer to both toggle the default spoiler and to
select a dashboard paint to color the calipers.

If you don't want to make the changes to the carcols.meta file yourself,
place the carcols.meta here:
mods\update\x64\dlcpacks\mpg9ec\dlc.rpf\common\data