In Chapter 27, Katniss and Peeta are interviewed by Caesar Flickerman, and a broadcast reel of the highlights of the event includes:
Things pick up for me once they've announced two tributes from the same district can live and I shout out Peeta's name and then clap my hands over my mouth.
So this announcement is certainly part of the official narrative. A situation with dual victors is unusual in any case and would need to be explained somehow.
What is not included in the highlights is that the rule change was rescinded for drama, and then reinstated at the last moment when it looked like there was going to be no winner. But this was in the original broadcast, since it's the basis for Haymitch's warning to Katniss in the previous chapter that she has embarrassed the Capitol. He says:
You're in trouble. Word is the Capitol's furious about you showing them up in the arena. The one thing they can't stand is being laughed at and they're the joke of Panem.
and she thinks:
Funny, in the arena, when I poured out those berries, I was only thinking of outsmarting the Gamemakers, not how my actions would reflect on the Capitol. But the Hunger Games are their weapon and you are not supposed to be able to defeat it. So now the Capitol will act as if they've been in control the whole time. As if they orchestrated the whole event, right down to the double suicide. But that will only work if I play along with them.
It's clear that the ruse with the berries was broadcast in such a way that people saw the Capitol backing down. But the loud announcement of the rule changing again from Claudius Templesmith - made at the moment they were about to eat the berries - was deliberately omitted from the interview highlights ("they end not with the announcement of our victory"). The revised official version of the narrative, with which Katniss and Peeta are forced to acquiesce, is that the double-victory rule was in place all along, and that taking the berries was part of a mad act of love, rather than being a response to the rule change made in order to force the Capitol's hand.
Of course, the authorities, including President Snow, are well aware of what was really happening. Their resulting attitude to Katniss, and hers to them, drives events in the following books.
In Catching Fire, Snow recaps all this to Katniss (Chapter 2), saying that
audiences in the Districts have taken her actions as a sign of successful defiance, despite the propaganda version. Also, the Head Gamemaker, Seneca Crane, has been executed for his "unfortunate sentimental streak".
All this only makes sense if the audiences had seen the Capitol back down, which implies they had seen the entire series of rule changes on first broadcast.
