It shouldn't take more than a few lines of code and $10 worth of memory to change the box: my phone can record 200 hrs of speech!
As has been stated already, the limitations are not technical. You can buy CVRs with as much storage as you want. The limitation is that pilots in the US insisted on a two-hour limit for privacy reasons, and that seems to have become a global standard — 30 mins is the minimum, 120 mins the norm.
Of course, none of this matters if someone on board disables it.