In-Depth - How to Edit Epson Media Files / Epson Media Installer

Become an expert at editing Epson Media Files / EMY.
You can edit and create EMY media files if circumstances dictate a change. This is a comprehensive look at editing and creating Epson Media Files for Epson desktop printers.
Epson created up Media Files EMY files to do a few things:
Be a media type setting
Contain advanced settings such as paper thickness, platen gap, ink density, and more.
Encompass color management information in very select applications - not in Photoshop, Lightroom, and other everyday apps you may use.
They also removed the now embedded settings from the driver where they used to be easily accessible. They are good in that the EMY is a one-stop-shop for settings and troublesome if you don't like dealing with the Media Installer application.
IMPORTANT POINTS
EMY files and made, edited, and maintained by software called the Epson Media Installer.
EMY files are designed to be made and maintained by you, the user. However, Red River Paper created a base set of files for your convenience.
You can edit the settings in an EMY file at any time. Save it as a new name if you want to keep the old EMY file intact.

[@Wairoakid]

Just a point Epson does document these printer setting that can be edited in instruction manuals when creating a 3rd party EMY profile. For the Surecolor P900 on page 204 it explains the settings that are relevant to the P900 in detail. However your explanation is much better by far