I posted this in the HubSpot community https://community.hubspot.com/t5/Account-Settings/Need-assistance-customizing-the-Right-side-CONTACT-Preview-in/td-p/1156377#M34928 and found that you can easily customize the lead preview window, but if the rep/user clicks on the contact record link (at the top of the window), it opens a contact preview that is not customizable. Allowing this will give customers much more control of what our reps see in Sales Hub and keep things that we do not want them seeing out of view. We are about to move from Velocify to HubSpot CRM, with all the bells and whistles (minus) service, and it is amazing but this will cause our reps to leave the Sales environment to update the Contact record.
Here is a video of what I am talking about (no sound)
HubSpot Sales CONTACT preview window - TechSmith Screencast
Thank you for your consideration and up-votes!