I use the pokesave at pokesheats. you can give it whatever IVs you want, but there is also a button to correct your PID, so if you have that checked it could change your Ivs to make it more legal. I think pokegen does some sort of similar thing.
I actually make a .PKM file then load it using pokeGTS and if I need to edit it I use pokegen.
I would recommend you make a .pkm file and go into pokegen and make surethe IVs are right before you load the poke on your game.