You do not need to reboot the host operating system or the server itself. The IMM operates independently.
Here is a short narrative based on that technical prompt. ibm imm remote control activation key
(Note: This is advanced; converting the ASCII key to hex bytes is not trivial. The web GUI is safer.) You do not need to reboot the host
If you possess a valid Activation Key for a legacy system, you must install it through the IMM web interface. ibm imm remote control activation key