If you find yourself needing to update existing code, add new variables, or even update external package versions, you'll likely want to edit an existing Blueprint. Follow these steps for editing a Blueprint.
Editing the Blueprint
Click the "Blueprints" navigation button on the side panel.
Next to the Blueprint that you want to edit, click on the "Edit" link, located on the right-hand side of the table under the column for "Action". By default, you'll land on the settings tab for the Blueprint. Every tab, except for Vessels, has fields that can be added or edited. These fields will look extremely similar to what you see when initially creating a Blueprint.
Edit any and all fields that need updating. You can make multiple updates across multiple tabs.
Once finished, click the "Save" button at the bottom of the page.
The Blueprint reference article contains details about how Blueprints work and what data gets stored.