Modern impatiens have been bred not to need pinching, as the plants decades ago needed. But yours may be stretching for light, tho you have grown them well. (Plus you've eaten all that yogurt!) You can indeed pinch them just above a set of leaves, which will leave you with a little "plant" in your hand, which you can then root and have double the number of plants. I have a friend who buys half the number of plants she needs every year, pinches off the top growth, roots them in soilless mix, fertilizes them and thus gets two for the price of one! So go for it.

Hey, those are some nice transplants! :)

Agree with above - probably just stretching for light. A pinch would help them branch out a bit more and keep them in check a while longer before planting out.

Once outside, no need to pinch nor deadhead.