How to use .PVRZ files?

Been playing around with NI, figured out with help how to replace .MOS images and use .PNG instead in the override, but I also see images stored as .PVRZ and when I try to follow the same procedure as I do with .MOS (saving a .png version with my changes and putting it in override while removing the .PVRZ from override) the game crashes when it gets to the point of opening the new image where the .PVRZ was. How do I replace those as they seem to work differently than .MOS despite many of them seeming to be exact duplicates of some of the .MOS files.