It seems to me that since the card is called “RUSH & ROTATION” that you are allowed to rotate troops. So if a single figure unit is alone in a front line trench, it may be activated along with a full figure unit several hexes back. The full figure unit moves first and ends adjacent to the one-figure unit and then the one-figure unit rotates back behind the lines adjacent to another friendly unit. This seems in both the spirit and title of the card to be allowable.
pmiranda wrote: Imagine unit A ends its move next to unit B. Can unit B, as part of the same order, now move elsewhere? (meaning unit A won't end the activation adjacent to a friendly unit)
The cards reads;
"Issue an order to 4 soldier units to reinforce success or rotate and pull back. An ordered unit may move up to 6 hexes, but must end its move in a hex adjacent to a friendly unit. Units may move through friendly units and terrain that is not impassable.
Units may not combat this turn." (emphasis added)
so whether a unit is adjacent to another at the end of the activation is irrelevant, the only thing that matters is it being adjacent at the end of the moving unit's move. If the adjacent unit subsequent moves, that doesn't retrospectively change the previous movement.