Reflexil, C# code injection in assemblies
Nice to see that some old ideas start to come to life! Reflexil is not exactly like my Patcher suggestion, but it has some features of it.
Here is the description taken from the Reflexil site:
Reflexil is an assembly editor and runs as a plug-in for Lutz Roeder's Reflector, a great tool for .NET developers. Reflexil is using Mono.Cecil, written by Jb Evain, which is a strategic library for the Mono project.
Reflexil is able to manipulate IL code and save the modified assemblies to disk. Reflexil also supports 'on the fly' c# code injection.
The sketch I had created for Patcher: