altering postscript code on the fly to get pure black and white

The PostScript Page Description Language

Hello, is it possible to alter postscript code (not manually, but on
the fly via a script or utility or whatever) before it is sent to a
printer?  I'm guessing not, but just thought i'd ask just in case.  I
want to convert the postscript code so that it prints pure black and
white, no greyscale.  Our users are complaining that the greyscale is
coming out too dim.  I was thinking about inserting the following line
at the beginning of the postscript stream,

{.999 lt {0}{1}ifelse} settransfer

Alternatively, I have considered setting up the printer queue so that
it prints to a postscript file instead of sending it to the printer
(This is done by setting the local port to a file path instead of an
IP address).  Then altering the file via some script, then sending it
to the printer.  Although, this really doesn't work well in a
multiuser environment as the file can get overwritten before it is

Please send any suggestions that might help, thankyou.

p.s. Some background on me, in case it helps.  I don't know anything
about developing printer drivers, but i know C++ and am willing to try
driver development if necessary.                                            
This has potential, but many operations including showpage reset the
default device transfer function.