Normally the Principle of Double Effect (PDE) is taken to be a permissive principle: it gives permissibility conditions for actions that are foreseen to have an evil effect. Roughly, the conditions are: the action is not in itself wrong; the evil is not intended as an end or as a means; and the evil is proportionate to an intended good.
Suppose that we adopt the thesis that refraining from an action is itself a kind of action, and that refraining can have effects just as any other action can. Call this the Refraining Parity Thesis (RPT).
Given RPT, it turns out that many of the actions that the PDE is used to justify are actually actions that the PDE actually requires. Suppose, for instance, that dropping a bomb on the enemy headquarters will cause a handful of civilian deaths but the deaths of the military leadership will lead to an early end to the war, saving thousands of civilian lives. Given RPT, consider the action of refraining from bombing. Refraining from bombing (considered maybe as an action of a military commander) has an intended good effect, the saving of the lives of the civilians near the headquarters, and an unintended evil effect, the deaths of thousands of civilians later. It is very plausible that the evil is disproportionate to the good, and hence PDE does not allow one to refrain from bombing.
There will, however, be cases where PDE allows but does not require an action. Suppose that I could save your life by jumping on a grenade. The PDE allows me to jump. The intended effect is saving your life by the absorption of kinetic energy, the foreseen evil is my death, and my death is not disproportionate to saving your life. But refraining from jumping is also permissible. The intended effect is saving my life, the foreseen evil is your death, and your death is not disproportionate to saving my life.
I don't know if RPT is true. I am inclined to think that refraining is not on par with positive action.