Painting and Deforming Alphas
Even if most functions used with Snapshot3D will be Snapshot and Union, keep in mind that most of the SpotLight 1.0 functions can be used on alphas.
As an example, you can use the Paint function with a Brush in RGB mode to paint white on an alpha to refine or change it. Also, you can hold the Alt key while painting to partially or even fully erase your alpha before painting on it further.
Obviously, functions like Restore, Clone, etc. will work perfectly with your alphas.