I have indeed had this technique work for me on multiple occasions. It is not that I have necessarily forgotten the "old" past, but it takes significant digging, and the original emotional strength tied to it is gone (completely or near-so). The "default" memory that comes to mind is the positive one. Or just none at all. The technique has definitely worked for me to completely deflate "past" events. They are now "ho hum, uninteresting" the times I do remember the "original".
Some times I will additionally also give myself the suggestion that I forget the "original" past event. This works quite well. (I could dig it up again with sufficient thought association, but the events really aren't interesting enough anymore to do so, having lost their impact.)
Speaking at least to the extent of my experience, I've found it easy to accept that this is possible on the fact that I have witnessed numerous times the distortive powers of emotion. Emotion can make an event something that would not otherwise be. I will give a hopefully not too controversial example. Seth says "if you expect an event to be sad, then it will be". As a teenager our family dog died, and at first (a few hours?) I was sad. Then I remembered this quote from Seth, and I thought long and deep about whether I was sad because I expected to be, or because it was legitimate to be. Now of course sadness is a natural human emotion like many others, all which have their own legitimacy and should be acknowledged and expressed. Having done so though, they tend to transform. They are also the effect of belief and thought, always.
It occurred to me that the present reality of the time was that my dog was having an absolutely brilliant time in whatever afterlife he was now a part of, and that is an extremely positive event. Yes I could dwell on his absence, but Seth teaches us to dwell on what we desire. I conducted an experiment with myself to see how short the stage of grief might legitimately be for my scenario in the absence of the belief that to grief for such and such a period was the "correct" and/or socially acceptable thing to do - to clarify, I'm not referring to fake grief, but to real grief perpetuated beyond its natural course by societal beliefs. I discovered, at least in my scenario, that the stage of grief was rather incredibly short (indeed short enough that it would appear unacceptable by onlookers). Since then I have had a similar response to other "tragedies". You might actually say a non-response or complete absence of grief. I should point out that in basically all of these I would say I was prepared quite well in advance psychically (even as others were shocked) and had fully accepted the eventuality and was actually even quite looking forward to the freedom that I knew the individual or pet in question was simultaneously looking forward to.
I also think about it in other terms as well. If everyone who remembered an event had their memory of that event altered, would not the event be different? Now I can hear talk of surveillance cameras and microphones but these cannot pick up on the energy and feel of an event, and even themselves are so extraordinarily limited. Watching someone point a gun at another and an emotional experience of terror and a gun being pointed and an emotional experience of fun play-acting make an entirely different event, no matter how convincing the actors.
It's well known that our own memory is incredibly fluid, a hundred people will have vastly different eye-witness testimony, this is demonstrated time and again in college law classrooms. It has also been revealed that while a memory is being recalled it is in fact "decoded" you might say, and once it is done being recalled it is once again restored. That is to say, it is not accessed from an unchanging bank of memory in the brain, but actually modified and re-written. (Selective long-term memory erasure seems to be possible in mice by inducing the recall of that particular memory, and then inhibiting a particular enzyme that aids in its reconsolidation, it spawned a lot of articles about the concept in humans such as this one.)
If everyone already remembers a different event than your own, why can't you yourself remember a different event than your own? Who says that their memory, or the new memory, is not just as valid? Although I can "think of" the "old" past memory with some effort, I can do the same thing with an entirely fabricated "memory", so who's to say the "old" memory isn't equally fabricated, as time is equally an illusion?
Having been educated in the mental realm that time is simultaneous (Seth), and having been educated in the realm of quantum physics that time is simultaneous (Einstein's theory of relativity), then whatever a camera might be able to capture is surely its own illusion.