That might be what they do. When you change chip families
MPLAB notices and asks to reprogram the ICD2 firmware.

The ICD*.hex files under C:\Program Files\MPLAB IDE\ICD2

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

I do not think that Microchip have released any spec for the 18F debugger
interface. I just assume it is very similar to the 16F87x, as it would
otherwise require a completely different set of software modules within
the
ICD2 to interface the two chip families, and that does not make a great
deal
of sense from the software development viewpoint.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.