adding constraints, editing bodies?

[mreinstein]

Is it possible to do these things from the existing UI, or would this be new feature work?

I was hoping to protoype a piston by:

1. creating some parallel rectangular bodies to act as a shaft
2. putting a rectangular body in the shaft (the piston)
3. setting their Inertia to Infinity to prevent rotation
4. attaching a spring constraint to the piston and the world, so it slides along the shaft

But all of these things require being able to edit various body properties, and linking constraints between bodies. I don't see a way to do that in the existing UI, but maybe I'm just missing it.