Looking at the Linux source "tpacpi::power" is in the "TPACPI_SAFE_LEDS" list; the setting mentioned in that thread only protects things like "tpacpi::dock_active", "tpacpi::dock_status1", etc.

I checked, and my kernel doesn't have that option, and I can change it just fine ("echo 0 >/sys/class/leds/tpacpi::power/brightness", as root of course).