My GLC350E doesn't has the blind spot assist feature. If it possible to activate this feature on my car ?
It is difficult to say without having the VIN number of your car. Can it be done? Yes. The question is what is already installed on the car. There are sensors all around the car that are needed to detect a vehicle. If your car does not have those sensors installed (most likely not) it will be to expensive to install it.
The bottom line is that Blind Sport Assist is not simply a feature that you Enable/Disable using a software.
If I have premium package in my car, can I add parking assistance in the future?