Andrea, you can't do this on early (pre-78) cars, because the torsion bars rest against the adjusting cams which in turn are fixed on the chassis. So before removing these cams (and thus taking off all tension from the bars) you can't remove (or at least practically refit) one or both suspension arms. On later cars, tension of one wheel's torsion bar is being taken entirely by opposite wheel's inner mounting, so when removing the complete rear suspension you have to deal with a closed system.
But this is not as hard to do as on later cars, or as on front torsion bars, and the special tool needed is very easy to make. Setting the ride height afterwards is equally easy.
Paul, Renault's manual says exactly this: release tension from each bar, remove it, and remove each suspension arm individually.