If I'm not mistaken cut rifled can be fluted after but not so on hammer forged or buttoned rifles barrels, by that I mean it can be done its just not recommended.
My Bartlein was fluted by Kampfeld after it had already been cut,crowned,threaded, and chambered. It was then Melonited. It consistently shoots 1/2 MOA, most the time less. I've shot a 5 shot group one time that measured .14 it was the best 5 shot group I've ever shot from any rifle.