You will have to expand the pokémon data structure so that the six base stats will all be halfowrds (16-bit) instead of bytes (8-bit). You will also have to change the references to the data table because each entry (i.e., each pokémon's data) will now be longer. Then you'll have to hunt down every single routine that loads a pokémon's base stats and change them so that each one loads halfwords instead of bytes. You possibly will also have to make some changes to these routines as they will be interpreting the data as bytes.
In other words, just give up.