To be fair, if you were to change the flooring in your bedroom and repaint the walls surely it's a bigish change.
Indeed it would be.
But it still wouldn't be a "new room", would it?
Nobody in their right mind would call it that. Whereas and extension, or removing/adding walls etc would constitute a "new room" in your house.
What you have described is a "redecorated/renovated" (or whatever) room, but not a "new" one. The same logic applies to the so-called "new" ITV regional news sets.
I'm a big fan of how the recycled sets now look, and would not dispute that the extent to which they have now been "redressed" is far greater than on any previous such occasion. But it still doesn't make the "new set" phrase any less incorrect/inaccurate.
I agree with those forumers who say that the joy of the 2004-style set is that it is so flexible as to be able to be rehashed every few years. The previous such rehashes were underwhelming at best though. Now is the best those sets have ever looked.