[timjver]

Simply twisting a single corner piece or flipping a single edge piece achieves that already, without having to mess with the stickers.

[DonHopkins]

Messing with the stickers makes it impossible to solve by simply twisting the corner piece back!

[dp-hackernews]

...the same is true for swapping two stickers on a corner.

If you alter the sequence of colours, you alter the finished pattern.

Therefore rendering the cube unsolvable.

QED

[dp-hackernews]

Not true.

Take a solved cube and twist a corner. Now jumble the cube and try to solve.

Do you see the problem Now?