Adding live rock to established tank

[boots]

Hi every one

I have recently bought my first mp40 and it's on it's way. How ever I have a large frog spawn that will be in the line of fire. So I would like to add a new piece of live rock to fill a void so that I will be able to move it back out of the way. My question is that if I add this piece will it throw my peramiters for a loop.

Thanks boots