Yes it's possible, there are several solutions:
- You can change CSS like this :
config.contentsCss = '/css/global.css';
- Use dataProcessor
- Change the enterMode
http://docs.ckeditor.com/#!/api/CKEDITOR.filter-property-enterMode
- Use BBCode plugin http://ckeditor.com/addon/bbcode
See the documentation : http://docs.ckeditor.com/#!/guide/dev_styles