What types of variables can be overridden by the system at runtime?

In Python, during runtime, various variable types can be overridden (changed) because the language is dynamically typed and supports modification of objects and their references.

Variable types that can be overridden during execution:

• Global and local variables: new values can be assigned at any moment.
• Functions and methods: the function definition can be replaced with another function.
• Classes and their attributes: class or instance attributes can be dynamically changed.
• Modules: modules can be re-imported or objects within a module can be replaced.

Example of overriding a function during runtime:

def greet():
    print("Hello")

greet()  # Will print Hello

def greet():
    print("Hi")

greet()  # Now it will print Hi

Thus, in Python, almost any variables and objects can be overridden during runtime, which provides great flexibility but requires caution.