There is no IPL requirement to load a new LMP key.
Passing the LMPKEYS option on the START command directs CAIRIM to read only the //KEYS DD statement.
This procedure will prevent the //PARMLIB DD and //AUTOCMDS DD from being read and thus the statements contained within from being processed.
After updating the appropriate KEYS member that is referenced by the CAS9 procedure (which executes PGM=CAIRIM), issue command:
S CAS9,,,LMPKEYS
This allows CAS9 to run and read only the KEYS.
Additional information about LMP processing can be found in the Common Components and Services for z/OS documentation, within section titled LMP and CAIRIM