You can't change the microcode of the PALM
processor. That would be like
changing the microcode of e.g. a MC68000.
It is, of course, possible to make a processor where the microcode can be
changed by the user. Many early graphics workstations (the PERQ, many of
the Xerox machines, etc) had microcode that was loaded from disk when the
machine booted. WCS (Writeable Control Store) options were available for
a few models of PDP11 to allow the user to write microcode.
-tony