OK, I replaced the joker80.exe on my website by one with adjustable piece
values. (If you run it from the command line, it should say version 1.1.14
(h).) I also tried to fix the bug in undo (which I discoverd was disabled
altogether in the previous version), and although it seemed to work, it
might remain a weak spot. (I foresee problems if the game contained a
promotion, for instance, as it might not remember the correct promotion
piece on replay.) So try to avoid using the undo.

I decided to make the piece values adjustable through a command-line
option, rather than from a file, to avoid problems if you want to run two
different sets of piece values (where you then would have to keep the
files separate somehow). The way it works now is that for the engine name
(that WinBoard asks in the startup dialog, or that you can put in the
winboard.ini file to appear in the selectable engines there), you should
write:

joker80.exe P85=300=350=475=875=900=950

The whole thing should be put between double quotes, so that WinBoard
knows the P... is an option to the engine, and not to WinBoard. The
numerical values are those of P, N, B, R, A, C and Q, respectively, in
centiPawn. You can replace them by any value you like. If you don't give
the P argument, it uses the default values. If you give a P argument with
not enough values, the engine exits.

Note that these are base values, for the positionally average piece. For N
and B this would be on c3, in the presence (for B) of ~ 6 own Pawns, half
of them on the color of the Bishop. A Bishop pair further gets 40cP bonus.
For the Rook it is the value for one in the absence of (half-)open files.
The Pawn value will be heavily modified by positional effects
(centralization, support by own Pawns, blocking by enemy Pawns), which on
the average will be positive.

Note that you can play two different versions against each other
automatically. The first engine plays white, in two-machines mode. (You
won't be able to recognize them from their name...)