Fabrizio,
I have committed a modification of topology.mac which
uses the new "style" option of plot2d. You can see it here:
http://maxima.cvs.sourceforge.net/*checkout*/maxima/maxima/share/contrib/sarag/topology.mac
There are some variables at the top of the file (SARAG_LINE_COLOR, etc)
which you can adjust. I wasn't able to find values which yield exactly
the same result as before, but I think it looks OK.
Aside from that the Maxima developers should decide whether
to support backwards compatibility for Gnuplot options.
By the way, how are you distributing SARAG ?
HTH
Robert