There are no problems altering existing structures like the Boss-Altar. They only have to change the 3D-model and the code behind.

The problem is inserting new structures in already explored areas.

Originally posted by Nameless:

Its 100% expectable that the people need to restart during Ea a few times

True. I started with H&H a new character and a new world and i don't regret it. Will do the same with all next major updates. There is a reason why the developer recommend starting a new world, even with H&H.