This MCU does not have Protection Module so apparently the only option is to use Memory Protection Unit.
Granularity of protected area is 32 Byte, so you cannot protect registers one by one. In this case it would be this register set:

Question is whether this is acceptable for your application.
Checker core is disabled/according LOCKSTEP configuration in DCF record, it is not is being started by software write as SIU_LOCKSTEP.