I would think that the various official pictures & portraits of the Queen would remain in place until she is laid to rest. They would probably be draped with black bunting or something similar.
To prepare for the death of the Queen, Charles probably already had official pictures taken. Those pictures would have been printed, framed, and packaged, prior to the Queen's passing. All that would be needed now is to ship the pictures to the various points around the world.
They've had years, even decades, to have everything ready and put into place.