I dont quite understand what you mean by “Safe mode” in bios mod/flashing…
Now i can tell you that any mod has its own risks… meaning that we can break any signature, code and that’s what will leave you with a broken system, not the flash itself.
I see you using OLD AMIBCP tool (had success in old Aptio IV and earlier Aptio V bioses) … not valid anymore for modern APTIO V bioses… and it can result in a “BAD” mod.
Usually, it’s not to change the value of the string, its her “visibility” only.
[TOOL] UEFI Editor - BIOS/UEFI Modding / BIOS Modding Guides and Problems - Win-Raid Forum
An advice, any user who engages in this MUST perform a full IC SPI dump of the system, in this mb particularly case the use on an SPI programmer like a cheap CH341A device, BEFORE any mod flash.
That’s all, good luck.