Hi all,
That pressurization recovery feature is the same in the Classic B747, but only whilst in one of the 'auto' modes.
If you were to operate the manual switch to 'open', the outflow valve WILL open, and you will depressurize, and the 10,000 foot warning horn will sound, (it's a 'dumb' horn, it always goes off at 10,000 feet, regardless of how you got there!).
Hope this helps,
Cheers