Is this an acrylic tank? If it is a glass tank you would have to cut the silicone adhesive that holds the brace in place, cut off some of it, then do a good job re-glueing it back on. I suspect the manufacturer found that that type of brace was necessary, so it would be risky to cut off that much of it. But, I also think the added cross brace would be adequate for restoring its strength. You would have to do that with the tank emptied of water or the brace might be a problem when you do empty the tank. (The stress on the brace would become compressive stress, and the brace could buckle.)
Wouldn't it be easier and better to switch to a canister filter?