It's easy enough to obtain a new license id (quick, automated process)
and make a little patch (the license numbers are declared at the top of
weather.h).
The only thing I'm not sure about is legal ramifications, though it
looks like TWCi has had the same license since 2008.
Index: xfce4-weather-plugin-0.7.4/panel-plugin/weather.h
===
--- xfce4-weather-plugin-0.7.4.orig/panel-plugin/weather.h 2011-02-02 15:31:29.0 -0500
+++ xfce4-weather-plugin-0.7.4/panel-plugin/weather.h 2011-11-05 21:04:15.214103897 -0400
@@ -21,8 +21,8 @@
#include libxfce4panel/libxfce4panel.h
#include libxfce4util/libxfce4util.h
#define PLUGIN_WEBSITE http://goodies.xfce.org/projects/panel-plugins/xfce4-weather-plugin;
-#define PARTNER_ID 1121946239
-#define LICENSE_KEY 3c4cd39ee5dec84f
+#define PARTNER_ID 1287437847
+#define LICENSE_KEY f5d0d6461b98f194
G_BEGIN_DECLS