You might be able to reprogram a Mt. Gox Yubikey with
ykpers or the gui version, but then it probably won't work with Mt. Gox.
UPDATE: After following the instructions here, I discovered the Mt. Gox Yubikey is protected by a "configuration protection access code."
From the manual:
Protection of the key and configuration data
Given the symmetric nature of the AES encryption algorithm, the
security of the Yubikey relies that the AES key is logically and
physically protected both in the key and in the server that verifies
The configuration data is updated via a configuration API, accessible
via the USB interface. To prevent unauthorized update, the
configuration can be protected by a 48-bit access code. If used, an
exhaustive search of all combinations would typically take some
100,000 years to perform. Furthermore, the Yubikey configuration data
is write-only, i.e. configuration data and the key can only be written
but not be read. This means that unauthorized update of the
configuration is an act of sabotage rather than a security threat.
The configuration data is stored in a non-volatile storage integral to
the microcontroller. A potential attack is to physically probe the
silicon or analyze the hardware behavior to potentially gain full or
partial knowledge of the stored secrets. However, such an attack would
require a complete break-up of the Yubikey, involving dissolving the
microcontroller chip encapsulation. Furthermore, very advanced
equipment is needed to probe the chip internals. Given the effort and
costs involved for such an attack, this is not considered a threat
given that just a single device will be broken.
So it should still be possible to "sabotage" a Mt. Gox Yubikey, no?
Hopefully the above description of how the Mt. Gox Yubikeys work helps you see why they can't use non-Mt. Gox Yubikeys: the "configuration protection access code" would no longer be Mt. Gox's secret.