Right now all customization I want from my vanilla WGR614L is getting rid of the LED.
Telnetting in /sbin has leddown as a symlink to acos_service, but it doesn't help much. I could not find the source for it.
It seems that /sbin/gpio should be able to set what individual LEDs do, but with one argument it always SIGSEGV, and two don't do anything. I tried the values from wlioctl.h, verbatim.
Turn out the gpio pins simply go from 0 at the right edge (LAN1 LED) up to 7 (power). Only the least significant bit of the value has meaning.
7 1=disable (sic)
6 1=enable
5 0=disable
0-4 0=green
I suppose the kernel handles blinking the WLAN LED, but it can be disabled. The WAN and LAN indicators can change color, but are probably hardwired (anybody has a hires shot of the board?) so I'm out of luck as far as annoying flashing is concerned.