The previous season I believe that regions were able to opt out of the Tuesday game and show their local sides the following night, showing the Wednesday network schedule a day early.
Not quite. Up until 1999, all the Champions League matches were on the same night so it was easy enough for one region to opt out while the network almost inevitably showed Man U - indeed, there was one example in 1998 when Carlton opted out for Arsenal only for a delayed kick-off meaning they had to show Corrie the following evening. But from 1999 it was complicated in that matches were now played across two nights. ITV had the Wednesday matches and ONDigital had the Tuesday ones, and although the Scottish regions were able to opt out if one of their teams was on the Tuesday (I remember them showing the NTAs on a delay at 10pm one yeat after a Rangers match), the English regions didn't.
The one you're thinking of is in 2001/02, when ITV had the Wednesday matches on ITV1 and the ITV Sport Channel had all the others, including all the Tuesday ones. Unfortunately, in the draw one week it came out with Liverpool vs Barcelona and Man U vs Bayern on the same Tuesday, and only Arsenal vs Deportivo on the Wednesday. There was no way ITV were going to miss out on that on the Tuesday, so in the end the network showed Liverpool vs Barcelona on the Tuesday, apart from Carlton, who showed The Bill and Millionaire, and then on the Wednesday Carlton showed Arsenal, while the rest of the network showed The Bill and Millionaire. The ITV Sport Channel showed both. But that only happened on that one occasion.
That was a great example of the failings of the ITV Sport Channel too in that the second a really big match turned up, ITV shoved it on ITV1 as well so there was no point in subscribing, which illustrates the problem of trying to run both a subscription sports channel trying to make money from exclusive content and also a free-to-air channel trying to make money from pulling in enormous audiences.
In 2002/03, after ITV Digital, when ITV still had the lot, ITV1's day was now Tuesday. There would be occasions when the regions would opt-out, I remember a Newcastle match one Tuesday on ITV2 which was also being shown on Tyne Tees in place of the networked match, which I remember because the ITV2 coverage began at 7pm but they started again at 7.30 when Tyne Tees joined, and at half time they did a report on Sunderland sacking their manager, which wouldn't generally have taken priority on a network show. But they never did it on Wednesday because Wednesday was a big night for ITV1 with Corrie and The Bill and they didn't want football two nights running. Of course the big problem was that ITV1 had regions but ITV2 didn't, so if they opted out on ITV1 it wasn't possible for anyone in that region to see the other match.
As I say, they tried to pretend in that case with Newcastle that they "weren't allowed" to show Wednesday matches on ITV1. That had a bit of merit the seasons before when there was a pay element, but not when the Wednesday matches were on ITV2. And, as I say, it ignored the fact they'd shown a Wednesday match on ITV1 about three weeks earlier, because it was Man U vs Juventus.