For the still shots, you might be able to do that in your NLE. You could try copying the clip to a new track, mask out the night background, move it to cover the space where the dwarf is, and feather it to help it sit with the rest of the background - or if there is a similar shot that shows the doorway without anyone there, even better to use that. Obviously, something like the opening door will require the mask to be adjusted frame by frame to follow the movement. For shots where the camera itself moves, that will be harder to pull off without looking funky.
Alternatively, you could mask out the entire doorway and replace it with a night background from another source.