Is it possible to replace the system class with your own?

Question

C++ / C#

In general, I don't really like the fact that the unit does not have simple things from later versions of c #, although adding some chips is quite simple by replacing the system class.
Is it possible to replace the system class or add a couple of methods to it so that they work for all objects in the project? If so, how? (talking about the object class)

Answer 1

What about extension?
How to: Implement and Call a Custom Extension Method
Why
replace
a system class...