Ok. So for some reason these people at Cosmos have not made the devkit available for people using the Express edition of Visual C# (No offense). So here's a tip:
1. Download the latest changeset from Cosmos.
2. Navigate to source\Cosmos\
3. Navigate to the folder with what you wanna change
4. As an example, I wanna change the protection status for two variables in Kernel.Heap, so I open the Cosmos.Kernel folder
5. Open the .csproj file and ignore any warnings
6. Select the file you wanna edit in Visual C#, and then change it.
7. Save it
8. Press "Build" on the top menu, and then "Build Solution", remember not to use debug
9. Go to the bin\debug folder, and then copy those two .dll and .pdb files.
10. Navigate to the folder where you installed Cosmos.
11. Go to "Tools"
12. Paste the .dll and .pdb files you copied earlier into these folders: Cosmos.Hardware, Cosmos.Hardware.Plugs, Cosmos. Kernel.Plugs, Cosmos.Sys.Plugs
13. Paste just the .dll into the folder GAC.
14. You are ready to go! In my example, I can now access the two "private" variables in Kernel.Heap.