As I mentioned, I have a different setup where the length of the stays is set and then I raise the mast from below to tension the rig. Perhaps, someone here uses a boat that's set up more like yours and can chime in.
I have sailed on other boats, including a DSII that did it differently, but can't quite remember the details. What I don't recall is any adjustments to the turnbuckles as part of stepping the mast.
As for the circular pins in general, they come in three flavors. Well, technically you could use an actual key ring for a fourth.
- a simple overlapping ring, from 1½ to two full turns: all parts fully align and you may need a fingernail to separate them to get started in engaging or disengaging the ring (the version with closer to two full turns is more secure)
- same, with two full turns but hammered flat (key ring style) so that the ends don't stick out
- like the first, but with one end bent in a slightly tighter curve so there's a gap between one of the ends and the main ring: when you twist that one one way, it will self-disengage, and to attach it, you only need to catch the end that points in.
- like the first, but one end is bent 90°: that makes it easy to push at that part to separate the windings to get it started.
Be aware that rings can come undone. I've sailed with one former forum member who told the story of a ring coming off, the mast going overboard and the boat capsizing. Wave action with continual loading and unloading of the rigging may contribute to that, but so can sheet's etc. that get snagged and pull a ring free.
Ideally you would tape these down (or, depending of where and how they are used, replace them with mousing wire). The latter is not practical for the clevis pins that hold the turnbuckles to the chain plates, but either wire or straight cotter pins with bent ends may be better for more stable applications such as preventing a turnbuckle from turning.
That said, I've never taped the rings for my cotter pins, but I make sure they are on the inside so that they are out of the way of the spinnaker sheets. I also generally sail for shorter distances/duration and have never seen an indication that any of them were tempted to work loose when it came time to disconnect them to take down the mast again.
The stays I have are adjustable, but only in terms of setting the length one time. They have a cylindrical knurled nut that you turn with your fingers to set the length and which is secured with a hex nut. To prevent the threaded rod from rotating in the fitting, the end has a ring in it, but you never need to remove that (there's never a need to rotate the rod, only the nut). The rings that I do remove are for the clevis pin that connects the adjuster to the chain plates.