I have the same problem. I don't need to rest or heal yet either. BUT from what you are saying, I need some kind of card I may get later with the white rest or heal icon and then I come back to this card and may then use the modifier while resting or healing? Which I suspect are probably either ways to get rid of red conditions or ways to get more cards to the action deck or both (I don't know because it's not in the manual).
There isn't a real good list of actions and how they work anywhere in the manual (or the reference card). The charitable way to view this is that they are afraid to give away too much information. The less charitable way to view this is that they didn't bother to give us a good thorough reference to action types and how they work.
Has anyone done this?
All actions are resolved using the same process. The success/failure of actions are different from card to card, so they can't really be any more specific in the rule book.
The icons just tell you what kind of action it is so you know what skills and items can be used for bonuses.