Or just print out QR codes that are bigger than the original and stick it over it... Or just print a new poster and paste it over... Iunno, I'm just not buying that this is a worthwhile vector.
It's interesting, but is it much of an attack? Ok, so you can determine what OS your phone is running, but you can do that by coding a QR code that brings them to a webpage that registers it with javascript; you need to direct them to a site regardless to collect your findings from this attack.
You might be able to attack a specific code reader, or a left-handed person who waves their phone over the dots in a different order? Or sneak a malicious code past QA and into the wild.
Step 1: Buy a ruler and put it in your pocket
Step 2: Whenever you see a QR code on a poster or sign, measure its width and make a note of it.
Step 3: Have a bunch of stickers printed in the most common widths, and carry them in your bag.
Step 4: Whenever you see a QR code on a poster, place a sticker with your fun/malicious code on top of it.