Is there any way or command to erase a T.A.R.D.I.S interior in singleplayer to do a custom build?

Or do I have to erase the whole interior by myself?

There's the /fill [x] [y] [z] [x2] [y2] [z2] minecraft:air

the x y z are the first coords and the ones with the 2 are the second coords

you can place a piece of obsidian under the door and then fill the interior with TNT

For now you have to remove it by other means but in Update 46 there will be a blank interior for custom interiors.