However, there is a huge difference between the way that this text is presented and what has been done in the other case. It is:
(1) at the start / end of the article rather than as part of a paragraph
(2) inside a box
(3) in an italic font
all of which help make it obvious to the reader that it is not really part of the article text itself.
Right, back to the substantive content (and I apologize for using English, I really do). I am concerned that simply changing the text in order to use the impersonal form of the verb while still leaving what are essentially instructions to editors in the middle of a paragraph would only half-solve the problem. I have now looked in more detail at what is done with the "eginyn Unol Daleithiau" stuff:
(1) As mentioned before, the instruction to editors is in a box at the bottom where it is obviously not part of the article text.
(2) Also, it seems that the content of that box is managed via a separate little "Nodyn" page, where it appears to me that if we wanted to change it subsequently it would be a single page to edit and would not involve re-editing the same hundreds of articles yet again.
If we decide that this text does needs to be on the article page, then I feel that the above approach is the way to do it, particularly in view of point 2, because (contrary to someone's fears that I am here to spoil things out of envy) I really have no interest in making this job end up consuming more of anybody's time and effort in the long run than it actually requires.