Coremods can be specified via the command line: fml.coreMod.load=<listofcommaseparatedclasses> This will help with developing coremods

common/cpw/mods/fml/relauncher/RelaunchLibraryManager.java

@@ -63,6 +63,42 @@ public class RelaunchLibraryManager
 
         downloadMonitor.updateProgressString("All core mods are successfully located");
         // Now that we have the root plugins loaded - lets see what else might be around
+        String commandLineCoremods = System.getProperty("fml.coreMods.load","");
+        for (String s : commandLineCoremods.split(","))
+        {
+            if (s.isEmpty())
+            {
+                continue;
+            }
+            FMLRelaunchLog.info("Found a command line coremod : %s", s);
+            try
+            {
+                actualClassLoader.addTransformerExclusion(s);
+                Class<?> coreModClass = Class.forName(s, true, actualClassLoader);
+                TransformerExclusions trExclusions = coreModClass.getAnnotation(IFMLLoadingPlugin.TransformerExclusions.class);
+                if (trExclusions!=null)
+                {
+                    for (String st : trExclusions.value())
+                    {
+                        actualClassLoader.addTransformerExclusion(st);
+                    }
+                }
+                IFMLLoadingPlugin plugin = (IFMLLoadingPlugin) coreModClass.newInstance();
+                loadPlugins.add(plugin);
+                if (plugin.getLibraryRequestClass()!=null)
+                {
+                    for (String libName : plugin.getLibraryRequestClass())
+                    {
+                        libraries.add((ILibrarySet) Class.forName(libName, true, actualClassLoader).newInstance());
+                    }
+                }
+            }
+            catch (Throwable e)
+            {
+                FMLRelaunchLog.log(Level.SEVERE,e,"Exception occured trying to load coremod %s",s);
+                throw new RuntimeException(e);
+            }
+        }
         discoverCoreMods(mcDir, actualClassLoader, loadPlugins, libraries);
 
         List<Throwable> caughtErrors = new ArrayList<Throwable>();