Put a default value list value based on the current users

Hi!
I've search all over the community but did not find the answer.

Here's the context :

I have an Object named Employee, for who I know his Office and his name.
Each M-files users is automaticaly created from this list.

When a user creates a new object named Assignement using a specific class, this class has also a property named Office.
By default, I would like to put the Employee's office as the default value. But the value could be modified if it's not the correct one for the user.

Automatic value of the property definition does not allow the user to change the value while he is creating the object.

So I'm not sure how to do this?

Thanks for your help!