visualforce

Made some progress on this issue. You can't actually customize the default ChangePassword and so what you could do is create your custom visualforce page with the controller to handle how you want your users password to be authenticated.

Next go to Personal setup => Email => Unfiled Public Email Templates. You can then customize the templates by removing the merge field {!Custom_url} and adding your link.

However, there is the issue of security here because usually the salesforce link the is sent to the user's email has an expiration time to it but with this approach I haven't quite figured out how this could be achieved. I guess I have my work cut out for me. Will do some more digging on this and add an update comment later.