X3 bios has built in FTP server so you should be able to just FTP in and make the alterations from there (I think the FTP settings are probably in network settings?).
Also, I can't remember how to do it (probably boot settings) but X3 bios allows you to select which xbe file it boots when it starts. Just point to your Avalaunch xbe and that should be it. If not, FTP a fresh copy over and point it to that.