Interesting question Hugh. As the Continuum doesn't say anything specific about it, the normal IRB Laws of the game apply - so I guess the answer is, yes they can move as long as they stay in the lineout. However, as a coach as well as a ref, my question would be why would you want them to move? My experience was you have enough on getting them to perfect the technique of synchronising throw, jump and catch while the opposition are trying to contest, without asking them to do it after changing position as well. Easier just to focus on getting the timing right and developing leg-power in your jumpers (which will carry over into your scrum and ruck as well). Dave Beal, Huddersfield RUFC.