Hello fc,
The best and most common approach is the first option, saving the old Hierarchy as an alternative hierarchy with a name like XXX_YYYY. I guess that the Application Control Manager solution can help you with this.
It will not affect performance if you don't query that alternate hierarchy, neither maintainability because you don't have to change those alternative hierarchies.
If you worry about managing Cube Views, you can automate it by creating an XFBR or GetMember rule that retrieves the correct hierarchy based on the Year.
Hope this helps!
