If doing online modification on primary CPU in HSBY mode then standby CPU will go to WAIT mode due to logic mismatch between HSBY CPUs.
To overcome this behavior , you can enable Allow logic mismatch box for "Standby on logic mismatch" setting on CPU HSBY configuration tab.
which will keep the state of Primary/Standby in case of logic mismatch till the number mentioned in the setting for example, if set to 20 means 20 modification will be allowed after that limit we need to sync the CPUs with same logic.

Note: In this case both CPU will run with different application/function. So it is recommended to keep identical application in both CPU to get same functional behavior.