cecil is awesome

awesomececil.cs

using System;
using Mono.Cecil;

namespace RenameAssembly
{
	class Program
	{
		static void Main(string[] args)
		{
			const string fileName = "MeshRenderer.Core.dll";

			var asm = AssemblyDefinition.ReadAssembly(fileName);

			foreach (var type in asm.Modules[0].Types)
			{
				type.Namespace = type.Namespace.Replace("MeshRenderer.Core", "TriangleNet.MeshRenderer.Core");
			}

			asm.Write("TriangleNet.MeshRenderer.Core.dll");

			Console.ReadKey();
		}
	}
}