We potted scarlet runner beans plants last week in several large pots. This week the soil settled a couple inches.
With tomatoes I know I could just top off the pots with more soil, and they will root from the stem. But not sure how bean plants behave.
Is it advisable to top these off with additional soil, or should I pull the plants up and repot?
Beans will be fine if you simply top up the pot.
While they need to be sown shallow, many gardeners pile up or mound the soil at the base of the young plants, mainly for better stability in bush beans, but also for runner beans. Unlike e.g. lettuce which will rot if transplanted deeper that before, beans are not sensitive to suddenly higher soil levels.
Yes I see your dilemma. Beans don't like to be checked in their growth and pulling this one at this stage with very little root established will be quite a shock; in fact if you were to germinate another seed the new one might easily catch up with a shocked bean messed with.
I see a few alternatives: first you could let the bean roots fill the pot and move it up to more soil when you can extract the root ball intact, or let the bean grow and then when the pot is filled and roots come out of the drain hole stand the whole thing on another pot full of soil to allow the roots to continue expanding, or let it be as is and start another to grow alongside in its own pot with generous soil.
My second suggestion makes me uneasy since you have the bean in a nice clay pot and balancing that on top of loose soil is inviting the loss of a good pot. My inclination would be my third alternative.
