Mike,
Assuming that what you describe is a cringle for another sort of
line that can act as a cuninhgam, and not a reef cringle, that will function the same way to you, but less effective because it is higher in the sail.
The cuningham is good because it pulls down on the lower side of the sail, but is also easier and faster to pull on a
line with a purchase than it is to pull the halyard.
Tension in light winds, release as much tension as you can, before you find the horizontal wrinkles, for low winds, so the draft moves aft. (see ion the video)
The only way to find out if you tensioned too much, is, by experimenting and by tensioning until you have long vertical wrinkles along the mast lenght.
But because your sail is being pulled higher, the lower part will have a tendency to create a "belly" bellow that cringle. Avoid that. With a cuningham you sacrifice a litle sail down by the tack cringle in exchange of better foil shape
If you look carefully in the video, it answers both your questions...
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