I'd wait until he was a little bigger to switch him to a finisher. 550 seems a little small to be fed a finishing ration. I've never known anyone to start feeding finisher that young except on dairy animals. He's still developing. Fat is the final step. He needs to grow his skeleton and muscle...
He needs mineral. What type of supplements are in his feed? If he is on a full feed finisher with a good supplement, just get him some type of finishing mineral.
Even cattle on mineral will tend to lick dirt/rocks a little at times. It's a survival instinct from way back before cattle were...
I cover the white spots on my calves with Vaseline. I wash the Vaseline out the following day with dawn dish soap and olive oil (the cooking kind) and then rinse them again with cheap hair conditioner. Just be really careful with where you're spraying the the dye.