Detach an entity from JPA persistence context

1 - Previously
Ok, you have designed a great domain model and then translete it to a database or, also much probably, have designed a great database and then generated the corresponding entity classes.

2 - Now
You have some GUI to get user input data. Easy. You create a new domain object (customer, product, bill or whatever else) and persist it through your favourite JPA engine.
Now you have some GUI that lists the available objects in your domain (again customer, product, bill or whatever else. I good idea could be obtain that objects in the way of domain object, I suppose for that reason you create a model, then you can change properties in some of that objects and store (persist) again those changes, so called merge changes.

3 - The question
Here comes the question. How can you detach an object from the persistence context? If you could get a dettached object you could modify its properties, then if the user agrees persist its new state or leave unchaged otherwise.

4 - The solution (or better say 'some of the solutions')
Detach an entity from JPA/EJB3 persistence context