RubyGS

require 'ruby_gs'

saved_game = SaveFileReader.read "/path/to/save/file.sav" # => SaveFile containing data representing the raw SRAM of your cartridge

saved_game.trainer_name = "Reich" # Note: Most fields that accept a string are limited to 10-character strings or less

saved_game.rival_name = "Bugs"

saved_game.team.pokemon[0].species = 25 # Change our first team pokemon's species to someone very familiar

saved_game.set_team_species 0, 25 # This is an alternative to the previous line except it also updates the team menu species

saved_game.team.pokemon[5].happiness = 255 # That's one happy Pokemon!

saved_game.team.amount = 5 # Annnnnnd now it's gone (Not really, it's just hidden from view)

hours = 78
minutes = 33
seconds = 12
frames = 20

saved_game.time_played = [hours, minutes, seconds, frames] # The amount of frames is not visible to the player and is rather inconsequential in general.

saved_game.item_pocket[3].kind = 1 # Change the 3rd item in our Item Pocket to a Master Ball. 

saved_game.item_pocket[3].amount = 255 # Gotta make sure we have enough for our journey.

saved_game.write # This will write your changes directly to the same save file you opened initially.

saved_game.write "path/to/other/save/file.sav" # This will write your changes to a different location.