My old friend Sébastien
pinged me a few days ago because he started to use Cecil. Let simply say that he was modifying some assemblies to circumvent a natural limitation of whatever program.
This long time Delphi user like to have a GUI for this kind of hack, so he simply started to write yet another plugin for Reflector
The plugin is only in a very early stage, but still, you can deal with primitives types and branches very easily.
You can find here
the mandatory introducing post for Reflexil. Even if it's in french, I bet you'll locate the binaries as well as the sources easily.