diff --git a/beets/library.py b/beets/library.py
index 945594307..fe4d9e0b5 100644
--- a/beets/library.py
+++ b/beets/library.py
@@ -414,17 +414,23 @@ class Item(LibModel):
 
         self.path = read_path
 
-    def write(self):
-        """Write the item's metadata to the associated file.
+    def write(self, path=None):
+        """Write the item's metadata to a media file.
+
+        ``path`` defaults to the item's path property.
 
         Can raise either a `ReadError` or a `WriteError`.
         """
+        if path is None:
+            path = self.path
+        else:
+            path = normpath(path)
         try:
-            f = MediaFile(syspath(self.path))
+            f = MediaFile(syspath(path))
         except (OSError, IOError) as exc:
             raise ReadError(self.path, exc)
 
-        plugins.send('write', item=self)
+        plugins.send('write', item=self, path=path)
 
         for key in ITEM_KEYS_WRITABLE:
             setattr(f, key, self[key])
diff --git a/beets/plugins.py b/beets/plugins.py
index 6a58777cd..b6fb157ca 100755
--- a/beets/plugins.py
+++ b/beets/plugins.py
@@ -17,9 +17,9 @@
 import logging
 import traceback
 from collections import defaultdict
+import inspect
 
 import beets
-from beets import mediafile
 
 PLUGIN_NAMESPACE = 'beetsplug'
 
@@ -40,7 +40,6 @@ class BeetsPlugin(object):
     def __init__(self, name=None):
         """Perform one-time plugin setup.
         """
-        _add_media_fields(self.item_fields())
         self.import_stages = []
         self.name = name or self.__module__.split('.')[-1]
         self.config = beets.config[self.name]
@@ -86,14 +85,6 @@ class BeetsPlugin(object):
         """
         return ()
 
-    def item_fields(self):
-        """Returns field descriptors to be added to the MediaFile class,
-        in the form of a dictionary whose keys are field names and whose
-        values are descriptor (e.g., MediaField) instances. The Library
-        database schema is not (currently) extended.
-        """
-        return {}
-
     def album_for_id(self, album_id):
         """Return an AlbumInfo object or None if no matching release was
         found.
@@ -297,13 +288,6 @@ def template_funcs():
             funcs.update(plugin.template_funcs)
     return funcs
 
-def _add_media_fields(fields):
-    """Adds a {name: descriptor} dictionary of fields to the MediaFile
-    class. Called during the plugin initialization.
-    """
-    for key, value in fields.iteritems():
-        setattr(mediafile.MediaFile, key, value)
-
 def import_stages():
     """Get a list of import stage functions defined by plugins."""
     stages = []
@@ -356,4 +340,8 @@ def send(event, **arguments):
     Returns a list of return values from the handlers.
     """
     log.debug('Sending event: %s' % event)
-    return [handler(**arguments) for handler in event_handlers()[event]]
+    for handler in event_handlers()[event]:
+        # Don't break legacy plugins if we want to pass more arguments
+        argspec = inspect.getargspec(handler).args
+        args = dict((k, v) for k, v in arguments.items() if k in argspec)
+        handler(**args)
diff --git a/beetsplug/convert.py b/beetsplug/convert.py
index c9645ae5a..031b4d839 100644
--- a/beetsplug/convert.py
+++ b/beetsplug/convert.py
@@ -174,13 +174,12 @@ def convert_item(dest_dir, keep_new, path_formats):
                 encode(item.path, dest)
 
         # Write tags from the database to the converted file.
-        if not keep_new:
-            item.path = dest
-        item.write()
+        item.write(path=dest)
 
-        # If we're keeping the transcoded file, read it again (after
-        # writing) to get new bitrate, duration, etc.
         if keep_new:
+            # If we're keeping the transcoded file, read it again (after
+            # writing) to get new bitrate, duration, etc.
+            item.path = dest
             item.read()
             item.store()  # Store new path and audio data.
 
diff --git a/docs/dev/plugins.rst b/docs/dev/plugins.rst
index cdea8938a..78b716d0e 100644
--- a/docs/dev/plugins.rst
+++ b/docs/dev/plugins.rst
@@ -297,41 +297,6 @@ This field works for *item* templates. Similarly, you can register *album*
 template fields by adding a function accepting an ``Album`` argument to the
 ``album_template_fields`` dict.
 
-Extend MediaFile
-^^^^^^^^^^^^^^^^
-
-`MediaFile`_ is the file tag abstraction layer that beets uses to make
-cross-format metadata manipulation simple. Plugins can add fields to MediaFile
-to extend the kinds of metadata that they can easily manage.
-
-The ``item_fields`` method on plugins should be overridden to return a
-dictionary whose keys are field names and whose values are descriptor objects
-that provide the field in question. The descriptors should probably be
-``MediaField`` instances (defined in ``beets.mediafile``). Here's an example
-plugin that provides a meaningless new field "foo"::
-
-    from beets import mediafile, plugins, ui
-    class FooPlugin(plugins.BeetsPlugin):
-        def item_fields(self):
-            return {
-                'foo': mediafile.MediaField(
-                    mp3 = mediafile.StorageStyle(
-                        'TXXX', id3_desc=u'Foo Field'),
-                    mp4 = mediafile.StorageStyle(
-                        '----:com.apple.iTunes:Foo Field'),
-                    etc = mediafile.StorageStyle('FOO FIELD')
-                ),
-            }
-
-Later, the plugin can manipulate this new field by saying something like
-``mf.foo = 'bar'`` where ``mf`` is a ``MediaFile`` instance.
-
-Note that, currently, these additional fields are *only* applied to
-``MediaFile`` itself. The beets library database schema and the ``Item`` class
-are not extended, so the fields are second-class citizens. This may change
-eventually.
-
-.. _MediaFile: https://github.com/sampsyo/beets/wiki/MediaFile
 
 Add Import Pipeline Stages
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/docs/reference/cli.rst b/docs/reference/cli.rst
index d479dcbae..4ee434237 100644
--- a/docs/reference/cli.rst
+++ b/docs/reference/cli.rst
@@ -361,7 +361,7 @@ Beets includes support for shell command completion. The command ``beet
 completion`` prints out a `bash`_ 3.2 script; to enable completion put a line
 like this into your ``.bashrc`` or similar file::
 
-    eval $(beet completion)
+    eval "$(beet completion)"
 
 Or, to avoid slowing down your shell startup time, you can pipe the ``beet
 completion`` output to a file and source that instead.
diff --git a/test/test_library.py b/test/test_library.py
index 3fa3d1173..41585d50b 100644
--- a/test/test_library.py
+++ b/test/test_library.py
@@ -29,6 +29,7 @@ import beets.library
 from beets import util
 from beets import plugins
 from beets import config
+from beets.mediafile import MediaFile
 
 TEMP_LIB = os.path.join(_common.RSRC, 'test_copy.blb')
 
@@ -958,6 +959,20 @@ class WriteTest(_common.LibTestCase):
         self.i.path = path
         self.assertRaises(beets.library.WriteError, self.i.write)
 
+    def test_write_with_custom_path(self):
+        custom_path = os.path.join(self.temp_dir, 'file.mp3')
+        self.i.path = os.path.join(self.temp_dir, 'item_file.mp3')
+        shutil.copy(os.path.join(_common.RSRC, 'empty.mp3'), custom_path)
+        shutil.copy(os.path.join(_common.RSRC, 'empty.mp3'), self.i.path)
+
+        self.i['artist'] = 'new artist'
+        self.assertNotEqual(MediaFile(custom_path).artist, 'new artist')
+        self.assertNotEqual(MediaFile(self.i.path).artist, 'new artist')
+
+        self.i.write(custom_path)
+        self.assertEqual(MediaFile(custom_path).artist, 'new artist')
+        self.assertNotEqual(MediaFile(self.i.path).artist, 'new artist')
+
 
 def suite():
     return unittest.TestLoader().loadTestsFromName(__name__)