Yeah, a cobbler really does more re-heeling and dress shoe repair.
The only way to de-yellow patent is to take it off and replace it. Doubt you wanna do that, tho. Just enjoy it, most people see yellowing as a badge of honor.
I have several Jordans that are deadstocked and yellowing. I freakin hate it.
now that you mentioned it, I dont see why more people just dont cover the yellowing on white patent leather with newer patent leather applied on top. for instance, on my 2000 space jams, a tiny section of it bubbled up due to me using retrobrite. now what I did was just scraped the tiny section with a razor blade and purchased a swatch of black patent leather. if my calculations are correct, ill be able to scrape the backing off of the new swatch to get it thin and then just glue it on top of the section where the old patent used to be.