Grind down the elements on a Yagi Beam???

I monitor and am a feed providor for Clark County Ohio and with the Marcs system, they are soon making a switch to the newer IP which is in a lower range 774. mhx specifically is where I will be monitoring. I use a beam Yagi in the 800 range and I bought a cell phone amplifier antenna that goes from 800 825 850 range, can I take these two antenna and trim up the element to be able to grab the signals better in the range I need.?? And what would one suggest I do when cutting or grinding down the elements. The 800-850 is a10 DB gain?

I am using 50 foot runs of quality RG6. Suggestion would be appreciated.

Grind down the elements on a Yagi Beam???