There is UART on that SPI+UART pad header.
Pinout is known: Support for Mikrotik Hap AC2
LHGG uses wil6210-lhg-span2.8.brd but I have no idea which one is used by your wap60g model, you need to dig that out from support file(That's the easiest as a most likely part of bootlog with that will be captured)
Also, for UART you need to modify the hard_config options.
Its not really easy to spot the seed as there is only one function linking to the one that does the decryption and that contains the seed.
You can use the one provided with ROS 6.43.12