Could it be done before flashing the A13 update?Flashing to both slots should not brick your device. The only thing that should cause a brick is if something goes wrong with the bootloader. This is the one disadvantage with the OTA - it only updates one bootloader slot, and it seems that once Android 13 boots, it's no longer possible to go back to an older bootloader.
So, if you want to be really safe, flash the updated bootloader to both slots, then update however you want. If it fails and switches slots, you should still be able to reflash.
I think of flashing only bootloader to both slots and then install A13 via PixelFlasher.
If yes, which are the right commands to flash only bootloader to both slots ?