https://www.googlesightseeing.com/2007/09/the-swastika-build...
1. Secretly repaint one wall of a house and redirect the qr code to a slightly different url
2. ???
3. ProfitThe issue with artsy QR codes often isn't the individual bit flips, but that they often include large areas of all black or all white which can make it harder for the reader to pick up the actually correct bits if the viewing angle and lighting aren't perfect. The standard includes 8 mask patterns that you can freely choose from, the intention being that you pick the one which gives most black/white variation in the final result, so there is as few low-contrast areas as possible. With improvements in cameras and processing built into QR scanners these days this is becoming less of a concern, but if you need your code to be reliably readable by older devices, probably stay away from the fancy tricks.
The fancy tricks are cool though, worth all the caveats if they match your stylistic needs.