They respond well to pruning, and will usually sprout from old wood if the need arises to cut them back hard. If the plants need to be shaped or reduced in size, the best time to prune them is immediately after they have finished flowering. It's also a good practice to pick-off the old spent flowers, as this not only improves the appearance of the plants it also reverts the energy of the plant to new growth and the development of next years flowers.

However....

I'm not growing Dorothy Wyckoff; descriptions I'm finding show the mature size as anywhere from 4 x 6, to 5 x 3...generally pieris is as least as wide as it is tall in my garden. Hopefully the mature size is close to what you have in mind, if it's much larger, you would be better off to chose a different shrub that will naturally stay close in scale to the size you need...much better than trying to force something to stay much smaller to fit your space by constantly pruning.

When you say to pull the spent flowers, do I just pull of the old bell flower, or cut the whole stem that they are hanging from? Thanks. I am new to this and can't figure out the technique to prune this shrub