A couple of questions. Why change his throwing mechanics now? How is it a liability? Has he recently been converted to OF or has he been playing that position for a while? How is his arm strength compared to others in his class?
Personally, I am not a big fan of making drastic changes in a kids arm slot unless he/she
is just, well, really really bad. In this case, unless he can't throw the ball where he wants to, why change now? I know a side arm guy is not typical profile for an OF'er, but unless he is more of a submariner, and he can throw, on target, why change? Maybe a consideration for a pticher?