This Extension does not change any of the core OpenCart files.
The Vitruvian SpeeDee Ship extension allows the site administrator to simply interface with a service that will calculate the fees that SpeeDee Delivery Company would charge. It also allows the Administrator to add a store Shipping and Handling fee to the shipping costs returned by the service. If you are doing business within SpeeDee Deliveries service area, I highly recommend looking into using their delivery service. Their pricing will surprise you.
This extension is free, but there is a $3.33 monthly subscribtion fee.