You are aware of how to use ildasm.exe to view the CIL code generated by the C# compiler (see Chapter 1). What you may not know, however, is that ildasm.exe allows you to dump the CIL contained within an assembly loaded into ildasm.exe to an external file. Once you have the CIL code at your disposal, you are free to edit and recompile the code base using the CIL compiler, ilasm.exe.
Also recall that reflector.exe can be used to view the CIL code of a given assembly, as well as to translate the CIL code into an approximate C# code base.
Formally speaking, this technique is termed round-trip engineering, and it can be useful under a number of circumstances:
You need to modify an assembly for which ...