writing to Essbase from OBIEE exist for many years...
In the past it was doing via a JSP page but since last year it's supported directly with a simple UPDATE statement.
Have a look at SampleApp 406 (current version), in the Essbase examples there is also the write back using the UPDATE statement.
Just keep in mind one thing: OBIEE is not supposed to be an entry form for Essbase or any other system, it can be used for editing values so you can dynamically change params for what-if calculations (running a calc script after updating a value) and that kind of things.
Thank you for your answer. I know that the functionnality exists for many years, but I exactly have in mind that it was just for params and can not be used as a template for sending data in the database, like Add In, smartview or planning. So you confirm what I thought but, the difficulty i have, is to explain why we can send data in essbase for params, and not for all database. So i am searching for constraints ou security reasons to answer...