I swapped the screen myself in my D300 without problem.
I've never touched a D600 so I can't say how good the viewfinder is. I think the D800 standard viewfinder screen is usable for manual focusing. If the viewfinder in the D600 is equal to the D800, it should not be a problem. Note that the green focus dot in the viewfinder works with MF lenses, but I don't think it's precise enough for critical focus at large apertures. At apertures in the f/8 region the focus dot shouldn't be a problem because DOF would allow enough focus tolerance.
For macro I prefer to use Live View for focusing. With Live View you can move the focus point to any spot on the image and zoom the LCD to 100% and more for focusing. That is much more precise than any viewfinder will give. Live View should work equally well on either the D7000 or D600.
Even though I'm comfortable focusing manually with the D800, I'd still buy a Katz Eye screen for it if/when the screen is available. For me the split image rangefinder in the screen is much easier to use than judging the sharpness on the ground glass of the standard screen.
Gary in SE Michigan, USA. Co-organizer of the Southern Michigan Chapter Nikonians membership - My most important photographic investment, after the camera. D4, D800e, D300, D90, F6, FM3a (black), FM2n (chrome) YashicaMat 124, Graflex Speed Graphic 4x5 My Nikonians Gallery & Our Chapter Gallery