Hi Shivam,
For changing the key-phrase you need to have JAVA stopped. Please refer to
https://help.sap.com/saphelp_nw73/helpdata/en/47/b08e68542e3378e10000000a421937/content.htm
Moreover changing it online and then restarting later may cause inconsistency as well. My suggestion will be to plan for a downtime.
Thanks,
Manas