Which structure pattern can be used to build the structure of a standard program?

As part of a standardization project, I have to develop the structure of a program. The program must work in such a way that you have different classes. The main classes have the functionality of the program. There must be an extension class for each class. This class is used so that the developers can do changes to the program using the extension classes. e.g. If I have a class called "Car" that has the method Motor, then I have to be able to override the Method Moto in the Class Car using an extension class called “Project_xyz_Car”. This means the Class "Project_xyz_Car" is used so that I can later develop customer-specific changes in code. My question: I would like to use structural patterns here. However, since I am relatively new to the subject, I would like to ask you for recommendations as to which pattern from the design pattern should be used here in order to achieve optimal performance and usability.