if the boom is out to starboard, I could turn to port and just leave the main sheeted out... then it would start to luff, right?
Of course, I would have to pull in the jib and use that to sail with to keep heading until the main went down...
Yes, true -- but your original uneasiness about the maneuver is fully justified. Trying to head up from a deep reach or DDW run is
a scary business in strong following winds. Your rudder is not as efficient, the boat is tippy and prone to sudden swerving, and the change in sail & keel function -- from a pure drag bag to a lifting foil, makes the boat surge in unexpected ways. If the waves behind are good size, rolling or broaching are quite possible. The boom's weight, slung way out, will make the boat heel as you turn. And what SD says -- your apparent wind will change directions & vastly increase in speed.
The trick is getting the boat thru the 3-5 o'clock zone as smoothly as possible, despite aft quartering seas and badly trimmed sails. If you have a swing keel or centerboard, I'd leave it mostly up until you are safe on a beam reach -- less likely to trip over it or round up too hard. Try to time your manuever to slide down the back of a passing wave, and have the crew ready to trim the boat for the next, inevitable broadside swell. Try to think a few seconds ahead, so all your gear is in the right place and bodies are moving as needed.
It's scary. When yesterday's strong winds tapered, we ran home wing&wing to the launch but had an accident. It was our first day sailing with the new halyard system (jammed knot at the mast top), & we couldn't unhook the knot & drop the main because it was under power. Can't blow the sheet cuz the boom is pinned to the shroud. Too late to head back for open water. "Ramming speed!" We beached at a stately couple knots.
No harm done, but it might have been ugly in bigger air.
Note to self! Head up while in open water, unhook the halyard knot, and either drop the main & reach home on the jib, or re-cleat the halyard minus knot, furl the jib, and be ready to sheet in to the centerline and drop main on approach.
Running is a weird business -- a mellow-seeming point of sail but full of dangers. The boat is in equilibrium, but it is an unstable equilibrium, like a bowling pin balanced on its top. When preturbed, the boat's manner can go crashingly bad in no time at all. Hey -- you are smart enough to see the danger BEFORE you crash into something. Definition of a good sailor!