In order to change attributes for specific objects on the list, you will first need to retrieve over association to get back the entire list of question objects related to your Enquete entity. After that you could loop through the list of questions, and for each question set the value of the association Question_Enquete to be equal to your Enquete, then commit the list.
The reason you do not see an option to set the association list when changing the Enquete entity is that the association is many-to-one. If the association were a many-to-many with the option selected for "both Enquete and Question entities to refer to each other", you would see an option to change the list of questions whend changing the Enquete entity.
Is this what you mean?