If you could control the umbrella with the same precision as your fingers, than I bet it would sound the same.
It seems that you are talking more about the TONE of the instrument, not the volume, which we all agree can't be changed on a harpsichord. As far as I understand it, tone is HOW the note sounds - harsh, round, full, pointed - no matter what the volume is. Very subtle differences, certainly, but I can hear the difference when my teacher demonstrates something. (And hopefully I can create those differences in my playing!)
On a piano, you vary the tone by varying your arm/finger weight. On a harpsichord I don't believe the tone can be changed except by the different mechanical stops. You might be able to create the illusion of tone changing by the articulation, separation and timing, but it's just an illusion.