Thanks to Lfd over in the PyS60 Forum here, I now have a better handle on view switching in Python. Now, when I execute a call-back function that needs to change attributes of the UI (from a listbox to canvas, for example) it's a simple task of wrapping the function with some state preservation and restoration code. 

What you see here is simple assignments, but exanding on Lfd's suggestion one could easily package all the attributes into a state tuple, push the tuple on a view stack, and pop views off the stack as needed.

Here is the simple case:

def takepic(filename):
    import camera
    # save UI elements
    oldBody = appuifw.app.body
    oldExit = appuifw.app.exit_key_handler
    oldFocus = appuifw.app.focus
    oldMenu = appuifw.app.menu
    oldScreen = appuifw.app.screen
    oldTitle = appuifw.app.title
    appuifw.app.title = u"Let us take a picture here."
    im = camera.take_photo()  # use all default values -- eventually this fn will change *.body into canvas control for viewfinder
    im.save(u'e:test.jpg')
    #restore UI elements
    appuifw.app.body = oldBody
    appuifw.app.exit_key_handler = oldExit
    appuifw.app.focus = oldFocus
    appuifw.app.menu = oldMenu
    appuifw.app.screen = oldScreen
    appuifw.app.title = oldTitle