Using Node Access Group with Primary and Alternative Hierarchies.

Requirement: Allow user to add/modify nodes only in alternative hierarchy. User should not be allowed to make changes to data from Primary Hierarchy directly/indirectly.

Solution:
1. Create a Node Access Group -> PrimaryRead.
2. Assign this NAG (Node Access Group) to the User.
3. Assign the same NAG to Primary Hierarchy with 'Read'.
4. Create another Node Access Group -> AlternativeWrite
5.Assign the NAG to user. 
6.Assign the NAG to Alternative Hierarchy with 'Add'.