The reason that "notthing changes" is that your "real" PLC is scanning its "real" I/O, and changing whatever value you put in with the "real" value.
If it can't communicate with the I/O modules that it "knows" should be out there (because they're in the I/O tree), then it reports the default, which is zero.
If you go into the configuration of each module, there's a checkbox for "Inhibit module" that should (I haven't worked with SoftLogx, but it does on a physical CLX) prevent the PLC from even trying to scan it's I/O, allowing you to write your own values.
Good luck