[XeTeX] unicode-math package and \UnicodeMathSymbol command

[Ed Morehouse]

i'm using the unicode-math package (2008/08/27 v0.3b) (which is really
fantastic, by the way) with the xetex from texlive 2008, and having some trouble
(re)declaring unicode math symbols.  for example, at the moment i would like to
use the vertical bar as a relation symbol and inverted exclamation mark as an
ordinary symbol.  but adding:

  \UnicodeMathSymbol{"0007C}{\vert}{\mathrel}{vertical bar}
  \UnicodeMathSymbol{"000A1}{\invexclam}{\mathord}{inverted exclamation mark}

to the end of my preamble doesn't have any effect.  however, if i change the
declaration for "|" and add one for "¡" in the unicode-math.tex file of the
unicode-math package, then it does what i want.  also, \input-ing a file
containing my unicode math symbol declarations in the same places that
unicode-math.tex and unicode-math-add.tex are \input in unicode.math.sty works
as well.

but what i would like is a way to make these declarations local to a document,
or better yet abstract them in a package, without editing the unicode-math
package itself.  any ideas?

-ed morehouse