Not sure if this will work but you can try to define a top-level package
function with the name trace() - I never tried it, chances are this won't
work though :) Another thing, if it's an AS2 SWF you can compile with MTASC
and specify your own function for trace. I haven't tried this, but maybe if
you redefine the trace() in HaXe, then it will override the default tracing
method... I also think that in AS2 you could redefine it through AsNative.
But I'm sure that other than that you cannot read from the output stream of
another SWF with SWF.