yes. just add an argument to the template tag in your sp theme…

registerLink=xxx

where xxx is the url you want the register button to go to…  so ie:

            sp_RegisterButton(‘tagClass=spButton spRight®isterLink=http://yoursite.com/register’, __sp(‘Register’), __sp(‘Register’));

So what is the purpose of the Registration Redirect option on the Login and Registration tab? Is that for after the registration is completed?

yes, for after registration or other action as indicated in the popup help…  understand how it can be confusing…