I don't really know liferay, but I assume that what you're trying to do here is adding custom metadata to an existing type. If so, yes it is possible by adding aspects and/or your own content type. To get started, I'd recommend Jeff's tutorial: http://ecmarchitect.com/archives/2012/01/09/1509 (careful there are several version. Pick the one in the 2014 update part)