First start with the window, most people will only have one window open, but when there are multiple windows, each can show a different scene.
win = bpy.context.window_manager.windows[0]
In 2.80 the current scene is a window property.
win.scene = bpy.data.scenes['Scene.002']
In 2.7x the current scene is a property of the active screen layout -
win.screen.scene = bpy.data.scenes['Scene.001']
But then what your sample code is trying to do is change properties of a visible editor, which isn't changing the scene, you need to dig a bit more for these properties. The relevant properties have also changed in 2.80.
In 2.80 the 3D viewport shading options are within the shading property -
for area in win.screen.areas:
if area.type == 'VIEW_3D':
area.spaces[0].shading.type = 'WIREFRAME'
area.spaces[0].shading.show_xray_wireframe = True
area.spaces[0].shading.xray_alpha_wireframe = 0.5
In 2.7x we can set wireframe display as part of the 3D viewport properties, the equivalent to wireframe x-ray is occlude geometry, which is an edit mode feature.
for area in win.screen.areas:
if area.type == 'VIEW_3D':
area.spaces[0].viewport_shade = 'WIREFRAME'
area.spaces[0].use_occlude_geometry = False