Hello,
Regarding the on entry/exit actions of domain specific work items, they will be shown if you switch the type of your work item to the default task type.
So the procedure would be to insert a domain specific work item and populate its attributes, then switch its type to default task the on entry/exit attrs will be presented, populate them and then switch the type back to your domain specific work item. Although a bit hacky it seems to work. However my opinion is to use script tasks before and after instead of the on entry/exit, since they are visible directly on the diagram and more clear to the reviewer.
I haven't migrated to latest realease of designer yet to try it out, however i think it will probably work the same way.