open the .objs in the file and when you save it back out you can use the original files rigging if you redo it in poser or studio to replace the old .obj

the easiest way would be to pose the car first and then flip it because poser and studio are very hostile to blenders rigging format and since i am not very well versed in poser and 0 in studio i wouldnt know the best way to convert it back