Assuming the host OS has the iLO driver installed (part of the ProLiant Support Pack), and you can connect to a host session (like Terminal Services) on the host, you can use the HPONCFG utility to effect the change.
See
http://www.hp.com/go/ilo --> Documentation --> "HP Integrated Lights-Out Management Processor Scripting and Command Line Resource Guide for HP Integrated Lights-Out versions 1.82 and 1.91 and HP Integrated Lights-Out 2 versions 1.1x, 1.2x, 1.3x, 1.70, 1.75, and 1.77" for information on how to do this. Also,
http://www.hp.com/go/ilo --> Sample Scripts for downloadable examples including changing iLO network settings. The iLO will actually reboot at the completion of the configuration change, but the host will remain unfazed.
