OneManMonkeySquad

Name the asmdef of your patcher Unity.SOMETHING.Codegen

Then edit the asmdef to include
"references": [ "Unity.CompilationPipeline.Common.dll" ],

I had to use my own Mono.Cecil dlls in the patcher directory, somehow it should be possible to reference the Unity.Cecil.dll etc.

Then use some code like this (Note at RpcPostProcessor.Process does the actual work here):