Ok let me write some hints for question 4- as I found them on searching through the user forum and so on...
I follow thread https://community.jboss.org/people/bpmn2user/blog/2011/03/30/jbpm5-example--human-task-forms-with-variables--workitems and get some useful information in it
So to summarize
4a => yes but it is no use modifying this file since you need to define your custom WorkItemHandler class in file CustomWorkItemHandlers.conf
4b => yes, you have to make a mapping between WorkItem Definition Name and which WorkItemHandler class is needed to be instantiated at runtime. The name should a valid WorkItem Definition Name deployed. I use drools-guvnor for defining my CustomWorkItem as stated in 5.3.0 User documentation (http://vimeo.com/26126678 skip to 2')
Is is possible to use an exploded war within JAS 7 ?
Another question is if I have some process definitions and I want to make only some code modifications in my WorkItemHandler, is it possible to update dynamically without need of JAS 7 restarting ? Before answering, let's assume say that there is no process instance running using the Custom Workitem.
Same question with process instances running and using the Custom Workitem?