Of course signs can be creatively adapted but that creativity is by necessity based on shared understanding. otherwise we're all the crazy people on the subway who talk to themselves.
Similarly codes can secretly shift the meaning of signs but the translation only works if the shift is predictable and stable. It can be extremely complicated but it can't work if it is totally random.
In QR publishing the meaning of the image, the relationship between the sign and it's meaning is decided elsewhere and can, therefore be changed without changing the sign (the actual QR image.) This potentially
- destablizes authorship -- the author is the one who controls the server where the translator lives rather than the person who designed the QR. In that sense the author can change over time.
- disrupts temporal nature of meaning -- what the image means can change over time in a completely unpredictable way,
- limits readership to those with the functioning tools -- if I don't have a device that works on the internet I cannot read the QR image and
- subverts permanence -- I can't read the intended meaning of the image without current access to the translator server. One could argue that writing limits access to the meaning of signs to those who are literate. But once learned, the ability to read is portable and, absent physical or mental deterioration, it is essentially permanent. Once I know how to read I can read anything in the language I know and I cannot be blocked from reading a text I can view.