LPC1343 Firmware Loading - Change drive label
This label is in ROM, and cannot be modified as far as I know. Only NXP can change this in their production process - but they need good reason ($$$$$) to do this.

The only thing you could do is to write your own boorloader. But given the small RAM (8k) and Flash (32k) of the device, this will be problematic, too - unless you have much space free in Flash.