Ronie,
It sounds like you have updated IPv6InterfaceInit to replace the default link local address (that's calculated from the interface's MAC address).
If that's true, I would not recommend doing that. The link local address is required by IPv6. You can add other addresses on top of that, though, which is what the ipv6 add command lets you do.
Please refer to RFC 4291, section 2.8. A Node's Required Addresses for further details.
Steve