Going Cayman - there are a bunch of good topics on tire and wheel insurance that you can find and read by searching but the short answer about adding the coverage later is "maybe". It depends on your dealer usually.

jcb - It is unclear if you have the coverage. If so it is going to be up to your carrier to determine replacement/repair. In the US most carriers rely on the dealer to make the call. Wheels can be repaired and again in the US there are lots of qualified repair shops.