I forgot about the JNLP file in the SweetHome3DViewer.jar that should match the one you change. Updating it in the jar file isn't enough, you will have also to sign again all the jars with your own software certificate to make it work. If you don't have a certificate, you may try also to simply remove the JNLP file from SweetHome3DViewer.jar. I think it will work but the JRE will display a warning.