You need to create a new solution and import the project files into that. Note that the project files were made with Visual Studio. I do not know what would happen if you import them in MonoDev; though they should be compatible.
You will also have to fix all references to required assemblies; but I assume you would know this if you are a coder and attempting to customize this code. Also check the build-settings. You will want to modify or remove the post-build events for example.
Why do you want to recompile the code? Can't you do what you need to do via scripts added to your Unity project?