In GSC shinies are based on stats, so if you use proteins and calciums and stuff like that will the Pokemon become shiny?
No. Pokemon can not become shiny after it was already shiny. If you get a shiny it can't become unshiny. In fact they arent even really determined by it's stats. They are determined by it's IVs.
This goes a little bit more in-depth about it: https://pokemondb.net/pokebase/106226/in-gsc-how-much-do-shiny-pokemon-have-dvs-for-each-stat