Hello, yes it is expected that normal board flashing utilities reject the modified image for most cases.
There are several ways to get around this lock depending on your specific motherboard.
I suggest you take a look at this post first to get an idea on what you might need to do.
If you’re on an Intel board without USB flashback support my best advice would be flashing the BIOS via Intel FPT by following this guide
It all boils down to what’s your specific hardware but there’s always a way to bypass flashing checks