chpark You need to add the margins in an image editor such as Photoshop. When adding margins, make sure to add the margins evenly on the top, bottom, left, and right. This will allow you to successfully retain the original mesh settings when you return to Spine later.
When you return to Spine, you will see the Images Resized dialog pop up, then select Keep size:
Then, in edit mesh mode, you can extend the hull of the mesh further out.
