gistfile1.txt

            var path = @"F:\Code\CecilTest\TargetLibrary\bin\Debug\TargetLibrary.dll";
            var moduleDefinition = ModuleDefinition.ReadModule(path);
            var typeDefinition = moduleDefinition.Types.First(x => x.Name.EndsWith("Class1"));
            var voidType = Type.GetType("System.Void");
            var voidTypeReference = moduleDefinition.Import(voidType);
            var methodDefinition = new MethodDefinition(".ctor", MethodAttributes.Public, voidTypeReference);
            typeDefinition.Methods.Add(methodDefinition);
            moduleDefinition.Write(path);