One sometimes need a special login page with its company logo, links and typolog : it's easy!
The principle is the same than for all files: your project's files overrides Nuxeo EP's.
Edit it and change what you want, just make sure you keep Nuxeo form, messages & login parameters.
The skeleton you want to keep is the following:
The CSS should be written into the HEAD.
Once you have a customized login page, you can ant your application and re-run jboss.