Yes, but not everything!
You can edit the whole project presentation as you want (project description, funds repartition, biography, title).
However you can not change the "rules of the game": the funding goal and the campaign duration cannot be updated after the campaign has started.
You can still add new rewards during the campaign. However, any reward that has already been chosen by a contributor cannot be edited anymore. If you must make a change, please get in touch with your coach.