A QR code is by nature a static thing.
When you generate a QR code you decide what the destination is going to be and that can’t be changed without re-generating it.
Services have started up that allow you to create dynamic QR codes however it’s not the code itself that’s dynamic but the destination.
I’ve set-up my own dynamic QR code service using the open source url shortening application yourls this piece of software allows you to set up your own url shortener.
Follow the directions included in the zip file to set it up on your web server, there is a typo on their website regarding the location of the config.php that was confusing until I read the ones included in the zip.
Once this is installed create a short url via the admin page and then use a QR code generator such as kaywa to create a QR code that points to the short url.
In the admin section you can change the final destination of the short url anytime you wish and you now have a dynamic qr code that can also generate stats.
Obviously this will only work for url type QR codes but I hope it’s of use to someone.