Edit. Oops! Typing the same time as Andrew.
My preference is to set up my tarp in an A frame but I like to have the flexibility to modify it if necessary.
I use a bowline to connect my guy line to my tarps. It's not a big deal for me to untie it if I need to move it but you could just tie the knot (not attached to the tarp), pull the standing end through the tie-out, and back through the loop of the bowline to secure it that way which makes it even easier to move.
I use the taut line as well but sometimes I'll incorporate a trucker’s hitch with it for the ridgeline if I'm attaching it to a couple trees.
This isn't text book but when I'm using my fixed lines with a shaped tarp and I need to shorten the line, I'll just tie a slip knot in a way that the loop will tighten around the stake. If you get it backwards, you'll know right away.
Some knots are stronger than others but I haven't had any problems with any of the above.
This is my list of knots that I use for ground shelters.
Bowline (to a tie-out or stake loop for fixed lines)
Clove hitch (use with a pebble to create new tie-out in tarp)
Prussic (attaching a tarp to a ridge line)
Slip knot (when I’m lazy to adjust a fixed line)
Taut line (end of guy line for non-fixed lines)
Alpine butterfly (I use the alpine butterfly and the taut line together to assemble the trucker’s hitch.)
This is obviously just one technique of many.
Edit again to add, I leave mine attached and move them as necessary.