diff --git a/overviewer.py b/overviewer.py
index dc4c5f2..9ab4019 100755
--- a/overviewer.py
+++ b/overviewer.py
@@ -269,6 +269,32 @@ dir but you forgot to put quotes around the directory, since it contains spaces.
 
     ############################################################
     # Final validation steps and creation of the destination directory
+
+    # Override some render configdict options depending on one-time command line
+    # modifiers
+    if (
+            bool(options.forcerender) +
+            bool(options.checktiles) +
+            bool(options.notilechecks)
+            ) > 1:
+        logging.error("You cannot specify more than one of --forcerender, "+
+        "--check-tiles, and --no-tile-checks. These options conflict.")
+        parser.print_help()
+        return 1
+    if options.forcerender:
+        logging.info("Forcerender mode activated. ALL tiles will be rendered")
+        for render in config['renders'].itervalues():
+            render['renderchecks'] = 2
+    elif options.checktiles:
+        logging.info("Checking all tiles for updates manually.")
+        for render in config['renders'].itervalues():
+            render['renderchecks'] = 1
+    elif options.notilechecks:
+        logging.info("Disabling all tile mtime checks. Only rendering tiles "+
+        "that need updating since last render")
+        for render in config['renders'].itervalues():
+            render['renderchecks'] = 0
+
     if not config['renders']:
         logging.error("You must specify at least one render in your config file. See the docs if you're having trouble")
         return 1
diff --git a/overviewer_core/configParser.py b/overviewer_core/configParser.py
index 412e1bf..dea9bf2 100644
--- a/overviewer_core/configParser.py
+++ b/overviewer_core/configParser.py
@@ -44,6 +44,18 @@ class MultiWorldParser(object):
     def set_config_item(self, itemname, itemvalue):
         self._config_state[itemname] = itemvalue
 
+    def set_renders_default(self, settingname, newdefault):
+        """This method sets the default for one of the settings of the "renders"
+        dictionary. This is hard-coded to expect a "renders" setting in the
+        settings definition, and for its validator to be a dictValidator with
+        its valuevalidator to be a configDictValidator
+
+        """
+        # If the structure of settingsDefinitions changes, you'll need to change
+        # this to find the proper place to find the settings dictionary
+        render_settings = self._settings['renders'].validator.valuevalidator.config
+        render_settings[settingname].default = newdefault
+
     def parse(self, settings_file):
         """Reads in the named file and parses it, storing the results in an
         internal state awating to be validated and returned upon call to
diff --git a/overviewer_core/settingsValidators.py b/overviewer_core/settingsValidators.py
index 7882d93..a378108 100644
--- a/overviewer_core/settingsValidators.py
+++ b/overviewer_core/settingsValidators.py
@@ -19,7 +19,7 @@ class Setting(object):
 def validateWorldPath(worldpath):
     abs_path = os.path.abspath(worldpath)
     if not os.path.exists(os.path.join(abs_path, "level.dat")):
-        raise ValidationException("No level.dat file in %r. Are you sure you have the right path?" % (abs_path,))
+        raise ValidationException("No level.dat file in '%s'. Are you sure you have the right path?" % (abs_path,))
     return abs_path
 
 
@@ -53,9 +53,11 @@ def validateNorthDirection(direction):
     elif isinstance(direction, str):
         direction = direction.lower().replace("-","").replace("_","")
         if direction == "upperleft": intdir = UPPER_LEFT
-        if direction == "upperright": intdir = UPPER_RIGHT
-        if direction == "lowerright": intdir = LOWER_RIGHT
-        if direction == "lowerleft": intdir = LOWER_LEFT
+        elif direction == "upperright": intdir = UPPER_RIGHT
+        elif direction == "lowerright": intdir = LOWER_RIGHT
+        elif direction == "lowerleft": intdir = LOWER_LEFT
+        else:
+            raise ValidationException("'%s' is not a valid north direction" % direction)
     if intdir < 0 or intdir > 3:
         raise ValidationException("%r is not a valid north direction" % direction)
     return intdir