normaly it should....allykat tested that codes.....and well....you only modify the look for you....in pokedex a hatched non-shiny will be non-shiny....so it is better doing it before egg hatches....well....i hope they will create an all poke shiny code which includes eggs, event/legendary and fossil ones (well....some legendary ones like the forrest trio or kyurem appear shiny....but others like zorua,tornadus and thundrus appear standart with the current shiny wild poke code, while Zekrom, Reshiram, Victiny and Zoroark let the game freeze with code on)!