Hi,
If you just want to add custom user profile properties, see User Profile Configuration. If you want to do more than that you can make your own ProfileView.aspx page in a custom project and use a post build event to copy it up to Web project replacing the mojoportal version of the page.
You can either always deploy your own custom build with your own custom features or you will have to restore your custom pages after upgrading to our release packages.
Hope it helps
Joe