When Mr. Hippo did a very prominent "smiley" on brand new hardware of my bag I literally run into the shop to ask if something can be done at all.
I was told that the hardware can be changed and it will cost some money, or scratches can be polished out by craftsman.
As for the change of the color of hardware - it is possible if the bag is blind stamped otherwise you would not want to do it as the color of hardware and the stamp would be visibly different.
Don't forget too the color of the metal part of the zipper pocket inside the birkin. The zipper would need to be replaced as well. Else, you will have a 2-tone metal hardware on your birkin (gold and palladium).
Sorry for the disfunctional association, but that´s like buying art that goes well with the colors of your curtains and sofas... If the original one, was PH, let it will be... And wait for a gold one... I´m not saying that if it will Hermès changing it will not be a real bag, but will not have the same "soul" as it was carefully made for the first time, it´s also like wearing color contact lenses... It´s like new rich women who go crazy with plastic surgery and change their original figure, instead of taking care and make it look better! You bought a PH, she will be PH for the rest of her life, because born like that, don´t get offended , please. this is just my point of view.
One day people will start asking for changing the leather colors also...