Jailbreaking is the process of allowing any code (without Apple needing to authorize/validate it) to run on your device. What you want to do is add functions/features to CarPlay. You can look into sideloading any carplay apps if they exist. 99% likely though that such apps cannot be sideloaded (carPlay is not a 3rd party app - it is built in feature that needs a tweak released that can only be allowed run on your phone if it is jailbroken after modifications.