So I just made a custom TARDIS, yeah? And I also make it able to be entered and exited, and when I go to the handle, it says "This Is Not Your TARDIS" and I need to know, how do I make it work? Same with the fly control panel, if it is possible to make those to work, then cool. If not then, well, that sucks.

 Nope doesen't work or help in anyway.

Are you in singleplayer? If you are then no clue how it's not yours but if you do the command that Sub said it should work.
Just make sure to also be looking at the tardis when you do it.

 Well it isn't saying the message anymore, but I wanted it to materialize and dematerialize.

Does anyone here know how to just get a blank tardis interior in single player.

there is currently no way to get a blank interior,  the best you can do is place some blast-proof blocks under where the door goes so you have something to build on, then stuff it chock full of your preferred explosives

 Thanks Ghost. I am brand new. But I have some pretty cool ideas.