The marked, slicktop and unmarked versions of the Caprice have been released:
File
2013 Chevrolet Caprice PPV - Slicktop and Unmarked - Blaine County Sheriff's Office (BCSO)

A fictional, California-inspired BCSO Chevrolet Caprice with Code 3 interior lights, with slicktop and unmarked configurations. A non-ELS vehicle featuring optional DLS support for light stages and traffic advisor patterns.
The models of the slicktop and unmarked versions are identical, their only differences are the liveries, carvariations.meta as well as the vehicles.meta to set which extras spawn.
To change which extras spawn by default, modify the extraIncludes and requiredExtra settings: Add all extras you want to spawn in an item in the extraIncludes and put one of those extras in the requiredExtras. All extras not forced to spawn will never spawn by default, with the exception of the radars in the marked unit, which will always spawn randomly.