Hingejoint: how to change axis correctly?

I made a physics based walker. It has four legs, it's pretty stable, but can't really turn. I want to make the rear legs rotatable a little bit on y-axis (the forward rotation is on z-axis).

It would be fine, if I could change the axis. Well, actually I can (through script), but if I do that, the rest rotation resets and 0 degrees will be at the point where I change the axis. So the leg will turn way too forward and not enough backwards.

How can I fix it?