Well, first you need to be able to work with a .MESH importer. The latest version of the OgreXMLConverter can convert a .MESH file back to a .MESH.XML file that can then be imported in some modeling tools via an Ogre Importer, e.g. Blender
I'm going to assume that after you export it, it's going to be a .MESH.XML and you're going to have to reverse the process by converting it from a .MESH.XML to a .MESH file