I've said this before but I can absolutely date to the day when I heard about the revamp - it was in the Sunday papers on 2nd June 1991, and I remember that because the very next episode on 6th June was the one where they featured records at number 41 and 42 and, stupid kid I was, I assumed that the policy of featuring records from outside the Top 40, as mentioned in the piece in the papers, was starting with immediate effect. Of course, it was just a coincidence that they were struggling to fill up the show and so ventured outside the Top 40. In any case, that was while Michael Hurll was still producing, so presumably the idea of the revamp was in the pipeline for a while.
There have been some odd transitional phases of Pops in between producers, June to September 1991 is one of them, plus also March to June 1997 when Mark Wells produced in between Ric Blaxill and Chris Cowey, and September to November 2003 when Dominic Smith produced in between Chris Cowey and the big revamp (it's almost exactly like that period, actually, given the big changes to follow).
Yeah those stand-in producers seemed to like to make their mark by making little tweaks to the format or presentation, even though they must've known they weren't going to be there very long.