adding to the offered experience...
you don't need to be fancy to get a good working adjustable ridgeline. I use Lash-It (1.8mm Dyneema) and lighter still dynemma core (I think) cord once sold as "Speers No Tangle" guyline. Do a semi-permanent attachment at one end, bring the working end down to the other end where it goes through some kind of loop (a soft shackle, or a biner) and then back out to the ridgeline where it's tied off with a taut-line hitch. The hitch holds both under tension and not, but can be slid up and down the ridgeline to make it adjustable.
For both I'd use what Ashley's book of knots calls the midshipmans hitch
(see #1855 down the page here
), and with the slippery Lash-It, do an extra wrap, repeating step #2 twice.
a no-knot technique replaces the hitch above with a biner where the ridgeline has wrapped 3 or 4 times around one edge of the biner. You can slide the biner along the ridgeline when the ridgeline is not loaded, and thus have a loop in the end of the working end of the ridgeline that clips into the biner.