+=item change_pkg
+
+Changes a package for this customer.
+
+Takes a hash reference as parameter with the following keys:
+
+=over 4
+
+=item session_id
+
+Session identifier
+
+=item pkgnum
+
+Existing customer package.
+
+=item pkgpart
+
+New package to order (see L<FS::part_pkg>).
+
+=back
+
+Returns a hash reference with the following keys:
+
+=over 4
+
+=item error
+
+Empty on success, or an error message on errors.
+
+=item pkgnum
+
+On success, the new pkgnum
+
+=back
+
+
+=item renew_info
+
+Provides useful info for early renewals.
+
+Takes a hash reference as parameter with the following keys:
+
+=over 4
+
+=item session_id
+
+Session identifier
+
+=back
+
+Returns a hash reference. On errors, it contains a single key, B<error>, with
+the error message. Otherwise, contains a single key, B<dates>, pointing to
+an array refernce of hash references. Each hash reference contains the
+following keys:
+
+=over 4
+
+=item bill_date
+
+(Future) Bill date. Indicates a future date for which billing could be run.
+Specified as a integer UNIX timestamp. Pass this value to the B<order_renew>
+function.
+
+=item bill_date_pretty
+
+(Future) Bill date as a human-readable string. (Convenience for display;
+subject to change, so best not to parse for the date.)
+
+=item amount
+
+Base amount which will be charged if renewed early as of this date.
+
+=item renew_date
+
+Renewal date; i.e. even-futher future date at which the customer will be paid
+through if the early renewal is completed with the given B<bill-date>.
+Specified as a integer UNIX timestamp.
+
+=item renew_date_pretty
+
+Renewal date as a human-readable string. (Convenience for display;
+subject to change, so best not to parse for the date.)
+
+=item pkgnum
+
+Package that will be renewed.
+
+=item expire_date
+
+Expiration date of the package that will be renewed.
+
+=item expire_date_pretty
+
+Expiration date of the package that will be renewed, as a human-readable
+string. (Convenience for display; subject to change, so best not to parse for
+the date.)
+
+=back
+
+=item order_renew
+
+Renews this customer early; i.e. runs billing for this customer in advance.
+
+Takes a hash reference as parameter with the following keys:
+
+=over 4
+
+=item session_id
+
+Session identifier
+
+=item date
+
+Integer date as returned by the B<renew_info> function, indicating the advance
+date for which to run billing.
+
+=back
+
+Returns a hash reference with a single key, B<error>, empty on success, or an
+error message on errors.
+