Q.dieffenbachia
I have a dieffenbachia plant that stands about 6 feet tall (one stalk). It is bigger and healthier at the top than the bottom. The leaves are bigger and closer together. It is top heavy and I have it tied to a stake. I wish it were shorter. I have read that you can start a new plant by planting a portion of stalk, keeping it watered and new roots will grow. My question is: Can I cut the top half of this plant and plant it the same way? Will it grow roots and live?

Yes, you can cut off the top and re-grow plants from both the bottom (rooted) portion and the top portion. Here is how to make cuttings from the top portion and root them:
https://www.gardeningknowhow.com/houseplants/dumb-cane/propagating-dieffenbachia.htm
Here's how to prune the bottom portion to shorten it:
https://garden.org/nga/searchqa/answer/78115/