I have a meterbase located on the side of the home. There is a 225A outdoor loadcenter located about 8" to the left of the meter. I am installing a 200A Transfer switch to the left of the loadcenter. Will I need to replace the 225A Main with a 200A main even though the transfer switch has a 200A main?
So you have a 225A SE load center is that correct? Where do you plan install the transformer switch then, ahead to the SE panel or after it?
It is a guess that you want to feed the SE load center.
Why don't you take an 8-1/2x11 piece of paper and draw schematic of your idea as to what you would like to do, scan it and attach a copy to your post.
It almost seems as though you want the ATS to be the SE due to the size of it