Unity 2019.1 or above
Starting from Unity 2019.1 you can enable/disable the Prefab Spawner assigning the command to whichever shortcut you want.
Open the Shortcuts Manager in Edit -> Shortcuts… and assign the command “Toggle Spawner” to your preferred shortcut.
Alternatively you can always press CTRL+SHIFT+E to toggle the spawner.
Other Unity versions
Just press CTRL+SHIFT+E to enable/disable the spawner.
CTRL + Mouse Drag
When you place a prefab, hold CTRL and start dragging the mouse horizontally to rotate the object or vertically to resize it.