Go language: How to change method implementation in run-time using reflection?

I have this type implementation:

type A struct{
  name string
}

func (a A) getName() string {
  return "My name is " + a.name 
}

How I can change implementation of method getName() for this type using reflection? For example, I want use next implementation instead of current:

func newGetName() string {
  return "test reflection"
}