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You can continue to keep the plant from drying completely.

Here is a link with more information.

https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/how-to-make-poinsettia-turn-red-make-a-poinsettia-rebloom.htm

The flowering and color change is actually triggered by lack of sunlight, darkness.
This is much more difficult to do with your plants in the ground.

Here is a link that explains the process.

https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/how-to-make-poinsettia-turn-red-make-a-poinsettia-rebloom.htm

It is possible for you Poinsettia to continue blooming into the Spring.
Here is an article with more information.

https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/poinsettia-care-after-christmas.htm

You can just prune it to shape as you like. You do not want to remove any more than 1/3 of the plant at a time, but other than that, you can remove growth as you need to.

This article explains the process with some diagrams in the Reflowering section:
http://extension.colostate.edu/topic-areas/yard-garden/poinsettias-7-412/

The time of darkness and temperatures are very specific to the reblooming of your Poinsettia.
Unfortunately there is no way to cheat the process.

https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/how-to-make-poinsettia-turn-red-make-a-poinsettia-rebloom.htm