Change picture for shader

Hello, sorry about my English. I have a material with shader is Transparent/Bumped Diffuse. So i want to change a picture NormalMap by code. How can i do it? Because if i have a shader with many components. I want to understand how can change a picture for each components by code. Thanks for help.

You can do this with any component of a shader, there is an example of how to change the normal map here.