You are mixing words here. I do not like it is different then believing.
So, Barry Sanders wears #20 up until being drafted #1 by DET and then you tell him sorry, that number isn't available.
Players are usually in a team's Hall of Fame before they retire the number. Why both? The jersey is just a symbol.
Then, we retire numbers long after a player has ended his career, and after someone else has worn it. Does that diminish the gesture any? Because really, it is just a symbolic gesture.
Hypothetical. What if Miguel Cabrera or Justin Verlander wanted to wear #6? Or even #23? I don't see an issue. It actually might immortalize that number even more.