I tried to do this per the documentation which says:
Change the meter in first bar to cover the duration of notes.
Change meter in second bar to meter of song.
Click on 1st bar meter and check Pickup Bar in dialog box.
What happens is that all notes are displaced by the difference in the first bar meter change and they never move back when Pickup Bar is selected. Also, this resets all clefs in the song. I tried moving the MIDI Part start positions to be at the point of the first pickup note instead of the beginning of the measure(thinking that the rests would not be counted in Score), but that didn’t help. It’s like the pickup bar is keeping the rests, even when Pickup Bar is checked in the diaglog box.
I usually don’t bother with any of that… I just Hide the rests before the pickup notes (then, possibly use the Hand tool to move the pickup note a bit to the left, and adjust the barline).
([Edit] I then also offset the bar numbers by 1, if necessary.)
(I think the documentation is presuming that you didn’t play the pickup bar as if it were a regular bar, with rests at the beginning . Btw, I got it work o.k. by following your own recipe of moving the notes, but only adding the “correct” time signature after having created the pickup bar)
I would just hide the rests, but it holds the space where they would be, and I am cramped for space on that line. I haven’t tried the hand tool yet. Don’t do this often enough to be good at it, unfortunately.
Don’t be frightened of the Hand tool, just select all the desired events with it, and drag!
Experiment also with dragging the barlines (the manual can help out as regarding different options using modifier keys while dragging)