It'll work just like that?
Yup. When it's done right, you now have an Eastern FH with the spin of a mild SW as well as a "longer line" to pull into the ball. In other words, not just a spinnier shot, but a heavier shot. All the other characterstics of your Eastern FH pretty much stays intact.
There's a bunch of neat biomechanical stuff involving SRCs and forearm pronation-supination-pronation, as well as how forearm affects potential laid-back position of the wrist . . . . but basically the idea is that Federer wants to "wind up" your forearm to the maximum during the unit turn. The more you wind up the forearm, the heavier your shot.
Inverting your racquet with an Eastern grip pretty much maxes out what his forearm will normally allow. And, as a result his Eastern FH is as heavy as can be without altering the swing plane itself.
Do you have any photos, or diagrams of this. I'm having a hard time visualizing.
I'm probably, as usual, overcomplicating it. You can use this slo-mo clip of Federer as a reference. Basically, watch how the racquet turns 180 degrees while he's holding it with both hands.
http://www.tennisplayer.net/public/..._evolution_modern_forehand_articlesample.html
1) Initially, both hands hold the racquet on edge or perpendicular with the ground. Thumb up.
2) As he begins to turn his hip, he rotates the racquet 90 degrees so that the racquet face is now "facing" the net. Thumb sideways.
3) He rotates the racquet another 90 degrees as he's completing the unit turn. By the time he releases his left hand, the racquet is on edge but upside down. His forearm is fully coiled. Thumb down.
Things to check for once racquet is reversed at end of unit turn:
1) Is racquet on edge and upside down?
2) Is wrist laid-back?
3) Is racquet tip pointing forward at about 45 degrees?
From there, then you do your normal swing.