I have the Samsung Galaxy S4 I9505 (with official KitKat 4.4.2) and I failed to detect NFC tags with display off / locked.
I tried the Modaco.Toolbox over Xposed framework, but does nothing.
Alternatively, do you know any unofficial ROM to do it? Maybe Cyanogen.Mod 11? I'm not sure it does.
Do you know how to turn off the camera sound?