Hey Pegleg
When you update the BIOS, your current 2600x will still be supported.
Generally, I don't update my BIOS unless something is wrong or I need a new functionality. You could always wait until you're ready to upgrade to the 5800x to perform the update
The instructions in the manual are pretty straightforward, and in the off chance that something does happen, your motherboard supports ASUS CrashFree BIOS 3, which can help to reflash BIOS if something doesn't work right.
https://dlcdnets.asus.com/pub/ASUS/mb/SocketAM4/ROG_STRIX_B450_F_GAMING/E14401_ROG_STRIX_B450-F_GAMI...Page 74 in the manual has instructions on how to use the BIOS flashing tool.