This functionality has been added to convert order notes into delivery instructions on Track 24/48 (non signature) labels. There are several steps that you have to follow:
Set up Prefix
One of the problems of using order notes to store the delivery instructions is that they are generic and contain other types of information.
1) Go to Settings > Shipping Management > Royal Mail Tracked
2) Enter a prefix that will be used to mark the note as a delivery instruction. Any note that starts with the specified text will then be then used to populate the Safe Place box. The maximum length (Excluding the prefix) is only 30 characters as there is limited space on the label.
3) Save the integration and then print the Tracked Labels
Edit Order Note
Currently most channels do not send over special instructions. However for custom website integrations it is possible to populate order notes automatically. When coding the script you need to ensure that the feed is prefixed with the same text that has been specified in the integration.
For direct orders you will need to manually create the order note by right-clicking on the order and selecting Edit Order Notes. Again you will need to start the note with the prefix.
Please see the following link for more information on Order Notes: http://www.linnworks.com/Doc/order_notes_order_management