i have been trying to create a rounded rear on the back of this platform. before the update that was possible but now i cant seem to do it any suggestions ???
Probably the morphing zones have been restricted in order to make all possible shapes look somewhat good. If you want to increase the range for morphing the bodies, you can do that by modifying the body’s .lua-file (look in Automation (install folder, not Documents)\assets\meshes\cars\small…). You find the morphing ranges in the “Bones” section of the file.
Modify the files at your own risk and backup the original files in case you break something. 
If you altered the morphing ranges in the lua file and you then made a car with a shape that was previously impossible, what would happen to the aerodynamic test results of the car? Would it take the results from the shape of car you have made, or would it take the aerodynamic results from the shape of car the original game would have with the sliders in their current position percentage wise. If it does use the actual car shape when it is beyond the vanilla lua file’s range how accurate do you think the aerodynamic model would be compared to when its measuring something within range?
Currently the aerodynamic model is just very basic: It just takes the base cD-value of the body and adds drag for grilles and wings, body morphing does not affect the cD-value. So currently the aero values would not change at all.
If the aerodynamic model can be made more detailed, for example if it could determine the cD-value from looking at the side profile of the car, I think it will be adaptable enough to calculate the correct value no matter how the shape has been made.