hello S.Harumoto,
there’s no way to add SBK key for your target.
as developer guide mentioned, Fuses and Security.
After the
SecurityMode(also known asodm_production_mode) fuse is burned with a value of 0x1, all additional fuse write requests will be blocked.
the best practice is to burn all the fuse values at once.
please dig into developer guide, Secure Boot.