Most if not all insurers will refund you for unused periods of prepaid cover, but usually levy an admin charge that varies from one company to another.
Slightly off topic but does anyone know if you are required to have your servicing done by a main dealer if you take out one of these extended warranties?
You really do get what you pay for when it comes to tyres. It's worth paying a bit more to get something that has been tried and tested such as Falkens or Toyos. Besides these are not oem sizes for the Zed.
Good luck with the new venture Fletch. I have never visited ESR but have purchased a number of items through mail order. As has been said already, this is a good earner so you really want to try and incorporate it as well as the servicing.