Upon multiple further viewings, I'm 100% certain that this disputed line is coming from Bono's raspy voice, sounding entirely consistent with Bono's banter immediately before it and sounding very different from the sound of Edge's softer, slightly-higher-pitched voice that can be heard introducing Sunday Bloody Sunday.
As for the line itself, the interpretation "I shouldn't have been called The Edge," does not make any sense conversationally. Bono is not called "The Edge," so it makes no sense to express dissatisfaction with and disown a nickname he's never been given... BUT...
That does sound like what he's saying.
As an expert in vocal imitation & caricature, and someone who has a very anal ear (pun intended)...
I very strongly contend that, what sounds like "I-shouldn't-have" (basically pronounced, "AHH-shun" with the "have" omitted entirely) is really "MAHH-gin," the ending of "imagine."
And "been" is really "being." Usually, continental Europeans pronounce "been" in almost the same way that Americans pronounce "being," with the long "e" vowel sound and the "n" sounding like an "-ng" ending, so we Americans can easily confuse those 2 words. However, I really think Bono is saying "being" here in this context.
The above reasons, combining to form an unquestionably strong gut feeling, convince me. Think about the joking tone Bono has throughout Popmart that is absent in the Unforgettable Fire, Joshua Tree, or Elevation eras. It makes perfect sense to me that in introducing Edge he would finally comment on how absurd it is that his mate's bloody name is actually "THE Edge," and that he would invite us to wonder how crazy it is to "own" and respond to a generic, universal description instead of a normal name.
