GÜ changes structural planning after work planning - legal consequences?

Hello,
our GÜ discovered during the input planning of our prefabricated house that the orientation of the ceiling beams on the ground floor must be rotated by 90 degrees, otherwise the structural "stability" (is that the right term?) apparently would not have been ensured. What legal implications does this have for us as builders? The floor plan / the house in the approval and working planning, which was also part of the construction contract, is different. Who is liable if problems with the structural integrity actually occur in the house at some point?
Isn't this theoretically a completely different house that is now being built?

Statics can be updated via supplements to the building application. As long as the changes only affect the interior layout, this should not matter for your building permit.

If, on the other hand, the exterior walls also need to be "rotated," a tectural application must be submitted – this is usually not a problem as long as building windows, etc., are not exceeded.

Liability lies with the builder & structural engineer – definitely have the complete statics including supplements/changes handed over to you, then you have the documentation.

In principle, it is not uncommon, in my opinion, for further consultations and possibly even changes to the statics to be necessary during detailed planning / workshop planning.

Who is liable if there are actually problems with the structural integrity of the house at some point?

Theoretically the structural engineer, which is why the change is practically being made right now to avoid this.

Isn't it in theory a completely different house that is now being erected?

From a structural point of view, it is no different than changing the direction of tension in a reinforced concrete slab. As long as the beams do not appear as a design element, I see the finished work as practically identical.