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Resonant frequency is proportional to the square root of stiffness over mass. Since we are increasing stiffness, adding a little mass should not be a problem.
It will make a difference especially if you put that glue on the surround edge! I read through the posts quickly and I see no mention of anyone testing the speaker with a calibrated microphone and software before and after the glue has been applied.
There will definitely be a change. But hey do what you want it is your sound.