We can assign rights in Planning at the individual dimension member level. Let us manually assign access of one of the dimension members and in the process, we'll learn what we need to know.
Go to Administration | Manage | Dimensions, select the 'Account' dimension, and expand it as shown in the following screenshot. We can see that even at the level 0, that is 'Sales', we can assign access.
Click on Assign Access to open a new window.
We have not assigned any users to the member 'sales' so far. Hence, we see no users in the assigned list.
Now, select 'Add Access'. We see the list of users as shown ...