Single Comment

'I'd like to set up a game where white chooses a piece to use and drops
  it on his first rank.  This causes an identical blue piece to appear 
  blue's first rank on the rotationally (or perhaps reflectionally)
  on symmetrical square...'

I propose to define an additional direction (here called 'mirror') that
links the squares from the first row to its symmetrical field. Example:

  (board
    (Board-Definitions)
    (links mirror (a1 h8)(b1 g8)(c1 f8)(d1 e8)(e1 d8)(f1 c8)(g1 b8)(h1
a8))
  )

Then in the setup phase you should be able to determine 'easily' by use
of
this additional direction, where related pieces are to be placed.

For different variants of symmetry use different lists for 'mirror'.