You can completely customize the layout of meals in your week, and have up to 9 meals per day. As an ETM Premium user, you can have different meals and nutrition profiles on each day of the week (allowing you to do things like have different nutrition targets on workout and rest days).
On the website:
To edit your Weekly Layout, click the "Edit Week" button in the top right (pictured)
Once it's open, you can customize the meals however you like. You can leave every day the same, or toggle the option to have a different layout for each day of the week (if you have ETM Premium). Here's an example of a layout that is customized with workout and rest days, and one cheat day that is left unplanned (so I can eat whatever I want that day):
Once you make the changes you want, click the "Apply changes to current and future meal plans" button. That will update the meals in your planner that are already existing. If you don't do this, only days that are generated in the future will have your changes.