Re: Donny's TOS Enterprise Interiors
If you are referring to the floor grate that GR is standing on, then it was there from the beginning, per this screencap.I don't know if there's anything useful in it, but there's also the introduction that Roddenberry filmed for the home video release of The Cage that was on the Enterprise sound stages. That was filmed either just before or just after The Voyage Home.
According to this screencap from the above-mentioned introduction of The Cage, the floor of the transporter room remained the same as it was pictured in TMP, although they seem to have added the raised segment all the way to the right of the room, which was definitely present in TNG.