As soon as my head stops spining I will put my 2 cents worth in.
I think the answer to your first question is no! (QW-403.18) a change is a change.
I belive QW 423.1 is explaining that when referencing a WPQ to a WPS,
if the WPQ base material is not listed in QW/BW-422 but has the same mechanical and chemical properties as the P-No listed in the WPS, then that P-No. my be substituted on the WQR.
If you read the table in lower part of QW-423.1 from left to right it gets a little clearer.
The left side being an example condition and the right side the rules governing it.
And then read on to QW-423.2