I am using the CC version. I am making a gunshot composition and I need to have a specific frame brighter. What should I do? Remember , there shall be only one frame , not all the clip with preferences!
Its been a long time since I've been in AE, but you could do this a few ways. You could physically layer a clip of the effect(with transparency) over the section you want to 'flash', or select the frame and tweak the saturation until it looks right.
Jim has a good point about splitting it into 3 frames. It will look much less harsh, but it will make timing a little more difficult. I would make the pre-glow focused in a certain area of the frame, the hot frame be completely covered by the effect, and have post glow be a diminished version of the hot frame. This will look the most natural, as it will look like your flash is actually originating from the end of the barrel (or whatever point you choose).
If I remember correctly, there is a masking function that you could use to achieve the pre-glow frame.
Ultimately, layering the effect on top would be easier because you're not working from pre-existing effects and you have the freedom to easily move and duplicate the clip.