I think that most common operation on alpha channel will be enabling/disabling it. It is aliased as on/off in convert utility (http://www.imagemagick.org/script/command-line-options.php#alpha).
with Image(filename="IMG.png") as img: img.alpha_channel=False # the same as running convert with option -alpha off
with Image(filename="IMG.png") as img: img.alpha_channel="deactivatealphachannel" # assumes you know the internals #or img.alpha_channel=ALPHA_CHANNEL_TYPE.index("deactivatealphachannel")
For more advanced usage there should be set_alpha_channel() method.