Everyone can share their opinion on this.
Personally, I support the idea of allowing restructuring from any level. It was as cool as the fix for one-sided units and normal roads. Once you try it, it's hard to give up. But playing with AI as an opponent doesn't appeal to me, as it's also somewhat a different game, just like in the case of HotA.
As I suggested earlier, you could include a flag in the HW Rules settings. This would be quite logical, considering that the restructuring functionality is based there.