I know it isn't funny now but later .. I did the same thing not long ago. What a crapass sinking feeling!
Fortunately I knew where all buttons should be and with rumble on(it vibrates when you hover over a button) I changed it back. Even though nothing showed on screen I knew it was there because of the rumble.
Funny now but then I thought well it is my 2nd Wii so imagine. I will try to get the steps for you.
Oh nevermind I just read your edit lol.
My little boy did the same - I found it out after spending hours trying to reset it. The was I got around the problem was by connecting the unit to a separate screen (an LCD) that then enabled the system to be adjusted back to 50Hz
all the best.
you should call nintendo they wii have it working in no time
Wii Games: Legend of Zelda: Twilight Princess, Heatseeker, Excite Truck, Wii Play, NHL 2k9, Super Mario Galaxy, Super Strikers Charged, Shaun White Snowboarding, The Bigs, Guitar Hero: World Tour, Ghost Squad, Call of Duty: World at War, Wii Sports Resort, Punch-out!
VC: Wave Race 64