Is it possible to change an instance's method implementation without changing all other instances of the same class? [duplicate]

Answer 1

Do Not Do This.

Changing one instance's methods is just wrong.

Here are the rules of OO Design.

1. Avoid Magic.

2. If you can't use inheritance, use delegation.

That means that every time you think you need something magic, you should have been writing a "wrapper" or Facade around the object to add the features you want.

Just write a wrapper.