Yes you can over apply CGM. When you do, the problem is the smell. You know about that already, but other than that, the CGM will not do any damage.

That smell is the smell of decomposing protein. It becomes a form of ammonia gas. When you smell ammonia, you are losing the nitrogen in that ammonia. If you want to try to capture it and prevent the loss of that fertility value, cover the area with a natural mulch or with dried tree leaves. They absorb ammonia.

You can over apply this as well as anything else although sometimes the only harm is to your wallet because you are simply wasting your money. However the odor also indicates that you are loosing nutrients to the atmosphere which is a form of pollution and can indicate that some of the excess nutrients could be flowing out through your soil and polluting the ground water.

I wouldn't worry too much about it. Chalk it up for lesson learned and move on. I never knew how much to use the first time either so it's trial and error to figure it out with my rotary spreader but you can't really cause much damage as you'd do with synthetic chemical. There's a lot of nitrogen in CGM so you can expect a lot of growth from whatever you have planted there. I know grass really respond to it. Just water them deeply and maybe the smell will go away.

Why can't you get rid of silver maple? Just wondering... There are better trees out there but I guess if it's about shade, that takes too long for a new tree to put out enough shade. I'm still waiting for some shade from mine...