This is a new cool feature I worked on with Brian and it’s coming on 6.1 as well as 6.0 EE SP2 and 5.2 EE SP6. With this feature you can add new struts actions to portal from a hook plugin and you can override any existing action with it.
There are two interfaces com.liferay.portal.kernel.struts.StrutsAction and com.liferay.portal.kernel.struts.StrutsPortletAction. The StrutsAction is used for regular struts actions like /c/portal/update_password and StrutsPortletAction is used for those that are used from portlets. More