Shift itself does not change perspective or magically refocus different parts of the building. A shift lens works by moving the sensor/frame to a different part of the lens’s large image circle while the camera stays level. That’s what lets you include more of the top of the building without tilting the camera, so verticals remain parallel.

If focus changes between the two setups, it’s mainly because the camera/lens axis was pointed differently before. When you tilt the camera upward and focus on the middle of the building, the distances to the top and bottom parts of the facade differ from when the camera is level. So the focus relationship can change due to geometry, not because shift itself alters perspective.

There can also be a small practical difference when shifted because the image uses more of the lens’s outer image circle. If the lens has field curvature or weaker edge performance, sharpness toward the shifted area may differ slightly. But with a good PC/TS lens, shift alone is not generally expected to cause a major focus change.