I did it. No problems!!!
I used a Tupperware orange peeler as a plastic opening tool and didn't touched any screws oder other inner parts.
I had to do it two times, because my old 4S 64GB has a broken WLAN Chip on the logic board, and my wifes 4S has broken her display glass. So I took her logic board into my 4S body. Now we have one running iPhone 4S 64GB instead of two broken phones.