My mech told me you should generally leave the fuel tap off when the bike is not running on any bike where the FT has been modified. (diaphragm removed)
Bit of a bitch isn't it?
Mine has been done probably because it was a track bike.
So it seems that you would not suggest the average person makes this modification?

Not really worth doing on a standard motor, and yes turn the tap off if its been done.

If you've done the HRC fuel tap mod, I'd suggest a quick release fuel connector. They're pretty cheap and you don't have to wake up in the night wondering if you've turned it off I removed my tap 'selector' so I fitted a QR. Also very handy for dumping fuel after a race/track day. Better safe than sorry!