I read that the film was darker and more violent before it was cut for release. I don’t know what specifically was in those scenes, other than that I thought the scene in the DVD extras with Sigourney Weaver pretending to seduce Sarris’ henchmen to distract them was one of those scenes that was cut to soften the film (creating the continuity error where her zipper is suddenly open and her bra is exposed for no apparent reason). If that wasn’t in your version, maybe you were indeed in a later round of testing.

I just re-watched the convention scene and I do see a cut where “Shut up” could have been (if it’s not one of those false memories we often have about movies). He turns to the screen, then it cuts to him walking toward everyone else. I think Guy saying “This guy can act” may be slightly joined in progress (unless Sam Rockwell just sort of contracted “This”), but the music doesn’t sound to have an edit, so the cut would have been made before scoring.