Yep nice little trick. Start position of that bookcase is against the wall. Use a script to move its appearance in front of the door and position your PC where you want them. Then and only then start recording. That way you can walk where the door was after moving the bookcase’s appearance back to match the position of its walkmesh.
Two things give it away. The PC never tries to walk where the bookcase is and (assuming it is supposed to be usable) there is no glow to the bookcase when the cursor passes over it unlike the door itself and the wall lever.
Like I said in my previous - paint a bookcase and move its appearance using
SetObjectVisualTransform(). You will now be able to walk through it. I know this from a module that I and a friend were building last year (now on backburner). During testing the PC accidentally walked through the bookcase and you couldn’t walk through where it had been originally painted in the toolset.