Re-number UCS Chassis

A UCS chassis can be renumbered when it is recommissioned into UCSM.  This procedure can be done from the CLI or from the GUI.  Note: This feature is available in 1.3(1t) and later, and 1.4(2x) and later.

From the CLI:
recommission chassis vendor-name model-name serial-num [chassis-num]   

From the GUI:
Step 1   In the Navigation pane, click the Equipment tab.
Step 2   On the Equipment tab, expand Equipment > Chassis.
Step 3   Verify that the Chassis node does not include the following:
    •    The chassis you want to renumber
    •    A chassis with the number you want to use
If either of these chassis are listed in the Chassis node, decommission those chassis. You must wait until the decommission FSM is complete and the chassis are not listed in the Chassis node before continuing. This might take several minutes.
Step 4   On the Equipment tab, click the Chassis node.
Step 5   In the Work pane, click the Decommissioned tab.
Step 6   For the chassis that you want to renumber, do the following:
    a.    Right-click the chassis and choose Re-commission Chassis.
    b.    In the Chassis ID field of the Re-commission Chassis dialog box, type or use the arrows to choose the ID that you want to assign to the chassis
    c.    Click OK
Step 7   If Cisco UCS Manager GUI displays a confirmation dialog box, click Yes.


Sources:
http://www.cisco.com/en/US/docs/unified_computing/ucs/sw/cli/config/guide/1.4/UCSM_CLI_Configuration_Guide_1_4_chapter36.html#task_D9A1BBEB813A40DEB845D1C2163EAF3A

http://www.cisco.com/en/US/docs/unified_computing/ucs/sw/gui/config/guide/1.4/UCSM_GUI_Configuration_Guide_1_4_chapter38.html#task_7CE3D4DF1CEF42A2A7BE144FEDF8DAB5