Title says it all. Not sure what's going on. It appears to save in options.txt, but it doesn't ever seem to matter.

Or change the key bindings of the other mods..

Also, this is problematic, as the default key of G sometimes interacts badly with other things that desire keyboard input. Chiefly, the search functionality in Creative Mode (mostly a nuisance) and the terminal in ComputerCraft (more troublesome). Oddly, even this interaction is intermittent.

Since it's not possible to save a new binding, one must remember to change the key binding each login.