punchings leveling

[Gerald Posey]

I hope there is room on the list for beginners.  I have rebuilt two uprights
and am now doing my first grand.  Of course, I have many questions.  The one
I wrestling with now is key dip and key leveling.  The information I have
says to decrease key dip by removing center shims.  If I do that, then they
won't be level.  To level them would mean putting the shims back in.  Is is
right to add shims to the front to decrease key dip?
    On a related note (?) what is aftertouch?  It sounds like an adjustment
of something after the key has travelled the required 3/8".
    Hopefully, my naive questions are easy to answer.
Gerald