There should be an "Edit Image" button when working with Textures with image-based shaders. This would open the image in the default photo-editing application (such as Photoshop), let you make edits, and upon closing/saving the file it would automatically load the updated image back into Vectorworks.   The current workflow is to exit the texture editing interface, right click the texture in the Resource Browser, choose "Extract Image", save the image somewhere on your hard drive, find