Yes it has been done before. It was done back in the days when taller the animal was, the better chance he had of winning.( Back then, I used to think that the guy who carried the poop shovel around the ring could have placed the class.... as you only had to line then up from tallest to shortest) It was called CHEATING then.... and it is called CHEATING now. I am a little surprised that someone would even consider this today in the era of moderating frame and thicker made cattle.
I would not recommend this to anyone. Firstly, I am sure it would be illegal at most any show... and why would someone even consider this for a 3/8 to 1/2 inch gain ... as opposed to being disqualified or even banned form the show. Secondly, you have to know how to attach the shoes properly. Cattle do not take to shoes as quickly as horses do, and I have heard of cattle that kinda ' goose walked" when the shoes were put on. I remember seeing one animal who had shoes installed... and one fell off in the show ring. Even the best walking animal doesn't walk the best with one leg shorter than the other three!!
I would suggest that you concentrate on trying to win the class that your steer legally belongs in. But then, that may be an old fashioned concept ie: winning honestly