BIOS flashback after installing an unsupported cpu?

Lets say the motherboard is an MSI MAG B650 TOMAHAWK Wi-Fi. It supports bios flashback, but doesn't have the newest bios installed for the new cpu. The cpu is 9800x3d. Would it make any difference to bios flashback before cpu installation or after? Other than it being less of a hassle to do it beforehand, and just assemble the pc and update the bios.

tl:dr what if someone who's lazy wants to assemble the pc and do the bios flashback afterwards, but the cpu isn't supported by the original bios version. The motherboard supports bios flashback from an usb drive.