All four Decal types can be created without leaving Blender.
The created Decals will be added to a temporary libary called Instant. It's meant to be a temporary holding place, to collect decals and experiment with various settings.
One or multipe non-decal objects.
Add Decal to Libarary
Use this tool to add an Instant Decal, or any other existing Decal to any unlocked library of your choosing.
Keep in mind