With OpenIV:

I. Copy the three Regina files to mods\update\x64\dlcpacks\patchday10ng\dlc.rpf\x64\levels\gta5\vehicles.rpf\
  
II. Copy vehicles.meta and place in mods\update\update.rpf\common\data\levels\gta5\  -OR-  copy lines in the vehicles.meta folder's text document and overwrite the REGINA entry in the .meta file.

III. Copy carvariations.meta and place in mods\update\x64\dlcpacks\mpchristmas2\dlc.rpf\common\data  -OR-  copy lines in the carvariations.meta folder's text document and paste in the .meta file.


