Hi LarsR,
I have not tried to manipulate the GP LED, if I find a document about it or if I'm able to manage it I will let you know, also here is a GPIO programing tutorial that you might find useful to handle the GPIO from Linux.
Intel Galileo - Programming GPIO From Linux
http://www.malinov.com/Home/sergey-s-blog/intelgalileo-programminggpiofromlinux
Regards,