Certainly - we encourage it. In fact, Hotdocs™ makes it easy to start with an existing template and create a new template with all of the necessary information for it to work with the existing set. This is an important technique and we're prepared a "how to file" for you to follow for simple text changes.
You can edit our templates to suit your needs if you like (this is within the terms of your license with us). The danger with this practice, though, is that when we update the set and send it to you, our template will overwrite your changes in the process. Better to make a copy of a template first and modify from there.
If you don't want to learn this new skill, we are happy to customize your set for you on an hourly rate basis. Contact us for a quote.