I would get the new DTC installed and configured before attempting to stop
using the old one.  Setup the new DTC with a new id of say DTC02 (if the only
DTC you have now is DTC01).  Once you have the ports configured and assuming
you have the same kind of cable connectors (25 pin, 3 pin, etc) you can
one-by-one disconnect and reconnect the cables to the new DTC.  This will
give you a new set of LDEV #s.  You may need to keep the old LDEV #s if you
have them buried in jobstreams for spoolfiles,etc. Even if you need to re-use
the existing LDEV#s, I'd still configure in the new unit and test it out
before switching.

A question: why change?  HP is dropping hardware support for more DTCs but
it's far easier to buy and install a spare 2nd unit rather than replace a
unit.

Wayne Boyer
Cal-Logic