Hi @richard.seguin,
Please check the schematics for the battery chassis below.
https://files.seeedstudio.com/wiki/Wio-Terminal-Battery-Chassis/res/WioTerminal_battry_650mAh.rar
It seems that the LEDs are not directly connected to the pins of SAMD51 and therefore you cannot turn them off using code.
I highly doubt that cutting the traces would make an impact on power saving, because these LEDs draw very little current.
And also, it’s not a very safe procedure to cut the traces physically.
Best Regards,
Lakshantha