Often times I want to keep the subdivision hull so I don’t have to work with so many vertices, but there are small changes I want to make without applying the subdivision modifier (easier time with weight painting and large form changes).
you could export it to 2.48, adjust it, and then import it back to 2.7. i think there are add-ons for importing and exporting from/to older blender versions. you don’t need to re-install anything, just make a separate folder within your main blender directory, download the zip instead of the installer, and unzip it into that folder. that is assuming you are using windows OS. I don’t know how the other ones work.
(edit) you can also export / import as an .obj file.
Yes, you can do it with Multires.
The thing is you can’t edit the Multires levels in EditMode, you have to go to SculptMode. It’s even easier to edit, you can be just as precise with a small GrabBrush, but can work on large scale areas as well. Sculpting in Blender is good.
Mind you, you can’t really export that to other appz without applying the Multires, and in turn getting stuck with the hiRez mesh.