perhaps you just swap the internal RJ-45 connections of a low- and high-power board and then check whether you still have full control over these.
if not, or if the selftest on startup (if enabled, that is) throws an error, you probably need to modify the ROM contents on the GPIB card.
tbh though ,i doubt that the GPIB will throw an error, simply because all 4 control processors on the power boards share the same partnumbers.