For 5.6.1 there has been conceptual changes to the way combo and tree nodes can be assigned for assets. This means the following rules apply
Read access allows the user to see the selected value and change the value to one the user has write access to
Write access allows the user to assign and remove the value to the asset
No access means the user can see the selected value, nor select it from the drop-down of selectable values
The breaking change in the above is relevant only if there are combo / tree values with different access levels for the nodes. Specifically it changes the behavior in two places
The user would be allowed to change the value of a field to a value the user had access to regardless of what was already selected. This is no longer possible and requires at least read access.
The access rights are now respected in the filters of the Media manager only allowing the user to see what they actually have access to.
There are some UX improvements in the pipeline around fields that has a value selected, but the user does not have access to it. This may give some save errors if the user tries to change the value of a field and the field already has a value the user does not have access to.