Sorry, I've no clue.

As it is, when I sit down outside to have my iced tea, I look over at the morning glories and see them waving at me from the top of the fishing line trellis I set up. Their arms are getting longer and longer, and I swear I hear them saying: "Help, I need to be grounded!" :-D

Yes, it is ok to not provide them with more climbing space. As they continue to grow, just wind them back down onto the trellis. You'll have to keep up with it, though, because they don't want to grow down, they want to grow up, so they'll turn right around and grow back up off the trellis if you let them. Every few days, just continue to wind them down along the trellis you've given them. Eventually, that trellis will get pretty full. You can always prune back the plant and let it fill out the trellis again....or just maintain the full trellis by cutting off the branches that start to reach out away from it....as the plant matures, you could end up with a tangled, gnarled mass of vines. I've seen jasmines grown this way for 5 years or so, but haven't seen how to manage them after that point. Maybe just cut way back and then let them fill out again. Or if you have a spot in the yard, you could plant them in the ground at that point, and get some new fresh young vines to grow in the pot on your porch.