---Could you briefly explain the whole procedures?
The process goes like this:
1. Disassemble the cover of keyboard.
1. Connect the keyboard with PC through special tool.
2. Burn the new firmware software into the keyboard chip by special software.
3. Assemble the S9 and do the test.
Above the process, we need to ues chip burner, PC, keyboard firmware.
The overall process, from disassemble to assemble, would take 1.5 hours.
---Do we need 31 tools for each S9?
No need, the tool and software is common on S9.
---How long will it take for not-trained engineer vs. trained engineer?
According to my experience, I think it will take 1.5 hours for one set of S9 to finish the whole process.
And you could also take advise from Sam-san, I think he has the related experience of disassembel board, which can help you to make decision.