Package initialization

[Helmut Eller]

What is the official way to initialize an ELPA package?  E.g. if the
package needs add a hook somewhere or change auto-mode-alist.

The manual says this about NAME-autoload.el files:

   They are typically used to autoload the principal user commands defined
   in the package, but they can also perform other tasks, such as adding
   an element to ‘auto-mode-alist’

Which seems to suggest that one should write some
;;;###autoload (progn ...)
somewhere that does the initialization.  Is this the way it should be
done?

And what is supposed to happen if two packages make conflicting changes
to auto-mode-alist?

Helmut