The only thing i can think of right now is to keep half of your object then mirror it or simply move faces to new object, then with the rect / rope tool select the verts that you wont be wanting to mess about with (down the middle between two meshes or by selecting individual verts) go to scale and scale them in on whichever axis runs along the front of the selected verts and click on that axis, then press 0 and scale them all in. That'l leave whichever face you want to mess with moveable.
The only tip i could add here for this method is to not scale multiple verts if they arent in a straight line, example if one offset above and one below you'l distort the mesh and the UV layout if you scale them. My reccomendation is to get whichever mesh you want to seperate set straight on an x y or z axis so that the mesh wont become distorted by this method.
If you leave the faces un 'welded' you might get a nasty unjoined line in game or in a render.
The only tip i could add here for this method is to not scale multiple verts if they arent in a straight line, example if one offset above and one below you'l distort the mesh and the UV layout if you scale them. My reccomendation is to get whichever mesh you want to seperate set straight on an x y or z axis so that the mesh wont become distorted by this method.
If you leave the faces un 'welded' you might get a nasty unjoined line in game or in a render.