Index: trunk/src/org/openstreetmap/josm/gui/MainApplication.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/MainApplication.java	(revision 4788)
+++ trunk/src/org/openstreetmap/josm/gui/MainApplication.java	(revision 4789)
@@ -102,4 +102,5 @@
                 "\t--[no-]maximize                           "+tr("Launch in maximized mode")+"\n"+
                 "\t--reset-preferences                       "+tr("Reset the preferences to default")+"\n\n"+
+                "\t--set=<key>=<value>                       "+tr("Set preference key to value")+"\n\n"+
                 "\t--language=<language>                     "+tr("Set the language")+"\n\n"+
                 tr("options provided as Java system properties")+":\n"+
@@ -194,9 +195,16 @@
         // Check if passed as parameter
         if (args.containsKey("language")) {
-            I18n.set((String)(args.get("language").toArray()[0]));
+            I18n.set(args.get("language").iterator().next());
         } else {
             I18n.set(Main.pref.get("language", null));
         }
         Main.pref.updateSystemProperties();
+
+        if (args.containsKey("set")) {
+            for (String i : args.get("set")) {
+                String[] kv = i.split("=", 2);
+                Main.pref.put(kv[0], "null".equals(kv[1]) ? null : kv[1]);
+            }
+        }
 
         DefaultAuthenticator.createInstance();