In the stock calendar app when you create a new event the calendar is listed in the top colored area. Touch that and it opens a drop down with all of your calendars. As far as I know you can only change calendars when creating a new event on your phone, not editing an existing one.
I do the same thing so my wife has my work schedule on her phone since it changes all the time
"Is life so dear, or peace so sweet, as to be purchased at the price of chains and slavery? Forbid it, Almighty God! I know not what course others may take; but as for me, give me liberty or give me death!"
-Patrick Henry, March 23, 1775