A Japanese magazine posted a video regarding Hyper Training, in which 3 Garchomp with different IV spreads were given a Silver Bottle Cap. This increased their attack stats to the same new value, the maximum attack a Garchomp with a beneficial nature (Jolly, Adamant, etc.) could have.

A Gold Bottle Cap was mentioned, hinting that such a thing could allow you to maximize more than one stat at a time, but it was left a mystery. Nothing was mentioned on how any of these caps are acquired (besides the one coming attached to Magearna) or if there's a limit on how many will be obtainable.