Can you debug applications by replacing DLLs?

Question

I was just wondering if it was possible to basically debug (I say that but I really mean reverse engineer w/ out disassembling) applications by replacing DLLs?

For example, if I wanted to know what data is passed in to a a function in a DLL by an application such as like:

public void doSomething(int val);

Could I possibly create my own DLL using the same .NET assembly information that simply does:

public void doSomething(int val) {
    MessageBox.Show("Application passed: " + val);
}

Or would the application notice that the DLL it's loading isn't valid? I'm asking this because I wanna try something and would prefer not to be wasting my time. Also, it seems to work in the case of Photoshop (I know it's not .NET) since you can crack it using a cracked version of amtlib.dll.

So, can you do this for .NET dlls also?