This extension will allow you to create your own pre-defined comments templates thus when you update the order status, you can simply select the templates to reply customer and update the status fast.

You can also use the place holders that defined the short message for examples:
You can use the macros
{num} - the order number
{sum} - order amount
{customer} - the buyer
In addition, you can use all of the available order fields, such as:
{email}
{telephone}
{invoice_no} and other

This support oc2.3 and oc3.0 version.

Installation just upload the zip file thru extension installer and set the access rights in user groups.

You will see the extension on left column under:
System > Localisation > Edit fastcomment for order
Which located under the "Order Statuses"