If you want an existing package to register as a WebVelocity one and as a result make it visible to the browser page, you can evaluate this script:
(Store.Registry packageNamed: 'Your-Package-Name')
propertyAt: #application put: true;
propertyAt: #namespace put: 'Your-Namespace';
propertyAt: #velocityThemeName put: 'Default'.
which I found when looking for the newApplication functionality in the image.