Put this in `Library/Application Support/Karabiner/private.xml`

private.xml

<?xml version="1.0"?>
<root>
  <devicevendordef>
    <vendorname>APPLE_INC</vendorname>
    <vendorid>0x05ac</vendorid>
  </devicevendordef>

  <devicevendordef>
    <vendorname>FILCO</vendorname>
    <vendorid>0x04d9</vendorid>
  </devicevendordef>

  <devicevendordef>
    <vendorname>KINESIS</vendorname>
    <vendorid>0x5f3</vendorid>
  </devicevendordef>

  <deviceproductdef>
    <productname>APPLE_INTERNAL_KEYBOARD_TRACKPAD</productname>
    <productid>0x0262</productid>
  </deviceproductdef>

  <deviceproductdef>
    <productname>APPLE_WIRELESS_KEYBOARD_0x022c</productname>
    <productid>0x022c</productid>
  </deviceproductdef>

  <deviceproductdef>
    <productname>APPLE_WIRELESS_KEYBOARD_0x022d</productname>
    <productid>0x022d</productid>
  </deviceproductdef>

  <deviceproductdef>
    <productname>APPLE_WIRELESS_KEYBOARD_0x0255</productname>
    <productid>0x0255</productid>
  </deviceproductdef>

  <deviceproductdef>
    <productname>KINESIS_ERGO_ELAN</productname>
    <productid>0x0007</productid>
  </deviceproductdef>

  <item>
    <name>Change Option_R to Enter on apple internal keyboard</name>
    <identifier>private.asf.internal-only.option_r.enter</identifier>
    <device_only>DeviceVendor::APPLE_INC, DeviceProduct::APPLE_INTERNAL_KEYBOARD_TRACKPAD</device_only>
    <autogen>__KeyToKey__ KeyCode::OPTION_R, KeyCode::ENTER</autogen>
  </item>

  <item>
    <name>Change Option_R to Enter on apple ext keyboard 0x022c</name>
    <identifier>private.asf.0x022c.option_r.enter</identifier>
    <device_only>DeviceVendor::APPLE_INC, DeviceProduct::APPLE_WIRELESS_KEYBOARD_0x022c</device_only>
    <autogen>__KeyToKey__ KeyCode::OPTION_R, KeyCode::ENTER</autogen>
  </item>

  <item>
    <name>Change Option_R to Enter on apple ext keyboard 0x0255</name>
    <identifier>private.asf.0x0255.option_r.enter</identifier>
    <device_only>DeviceVendor::APPLE_INC, DeviceProduct::APPLE_WIRELESS_KEYBOARD_0x0255</device_only>
    <autogen>__KeyToKey__ KeyCode::OPTION_R, KeyCode::ENTER</autogen>
  </item>

  <item>
    <name>Change Option_R to Enter on apple ext keyboard 0x022d</name>
    <identifier>private.asf.0x022d.option_r.enter</identifier>
    <device_only>DeviceVendor::APPLE_INC, DeviceProduct::APPLE_WIRELESS_KEYBOARD_0x022d</device_only>
    <autogen>__KeyToKey__ KeyCode::OPTION_R, KeyCode::ENTER</autogen>
  </item>

  <item>
    <name>Change Application (context menu) to Enter on any external keyboard</name>
    <identifier>private.asf.non-internal.context-menu.enter</identifier>
    <device_not>DeviceVendor::APPLE_INC, DeviceProduct::APPLE_INTERNAL_KEYBOARD_TRACKPAD</device_not>
    <autogen>__KeyToKey__ KeyCode::PC_APPLICATION, KeyCode::ENTER</autogen>
  </item>

  <!--
      https://github.com/tekezo/KeyRemap4MacBook/blob/master/src/bridge/generator/keycode/data/ConsumerKeyCode.data
      has the key defns used here:
  -->
  <item>
    <name>Change PrintScreen/SysReq (F13) to volume down on any external keyboard</name>
    <identifier>private.asf.non-internal.f13.volume-down</identifier>
    <device_not>DeviceVendor::APPLE_INC, DeviceProduct::APPLE_INTERNAL_KEYBOARD_TRACKPAD</device_not>
    <autogen>__KeyToKey__ KeyCode::F13, ModifierFlag::NONE, KeyCode::VK_CONSUMERKEY_VOLUME_DOWN</autogen>
  </item>
  <item>
    <name>Change Scroll Lock (F14) to volume up on any external keyboard</name>
    <identifier>private.asf.non-internal.f14.volume-up</identifier>
    <device_not>DeviceVendor::APPLE_INC, DeviceProduct::APPLE_INTERNAL_KEYBOARD_TRACKPAD</device_not>
    <autogen>__KeyToKey__ KeyCode::F14, ModifierFlag::NONE, KeyCode::VK_CONSUMERKEY_VOLUME_UP</autogen>
  </item>

  <item>
    <name>Change Ctrl + Scroll Lock (F14) to Play/Pause on any external keyboard</name>
    <identifier>private.asf.non-internal.ctrl-f14.play</identifier>
    <device_not>DeviceVendor::APPLE_INC, DeviceProduct::APPLE_INTERNAL_KEYBOARD_TRACKPAD</device_not>
    <autogen>__KeyToKey__
    KeyCode::F14, ModifierFlag::CONTROL_L | ModifierFlag::NONE,
    KeyCode::VK_CONSUMERKEY_MUSIC_PLAY
    </autogen>
    <autogen>__KeyToKey__
    KeyCode::F14, ModifierFlag::CONTROL_R | ModifierFlag::NONE,
    KeyCode::VK_CONSUMERKEY_MUSIC_PLAY
    </autogen>
  </item>

  <item>
    <name>Change Ctrl + PrintScreen/SysReq (F13) to Previous Song on any external keyboard</name>
    <identifier>private.asf.non-internal.ctrl-f13.prev</identifier>
    <device_not>DeviceVendor::APPLE_INC, DeviceProduct::APPLE_INTERNAL_KEYBOARD_TRACKPAD</device_not>
    <autogen>__KeyToKey__
    KeyCode::F13, ModifierFlag::CONTROL_L | ModifierFlag::NONE,
    KeyCode::VK_CONSUMERKEY_MUSIC_PREV
    </autogen>
    <autogen>__KeyToKey__
    KeyCode::F13, ModifierFlag::CONTROL_R | ModifierFlag::NONE,
    KeyCode::VK_CONSUMERKEY_MUSIC_PREV
    </autogen>
  </item>

  <item>
    <name>Change Ctrl + Pause (F15) to Next Song on any external keyboard</name>
    <identifier>private.asf.non-internal.ctrl-f15.next</identifier>
    <device_not>DeviceVendor::APPLE_INC, DeviceProduct::APPLE_INTERNAL_KEYBOARD_TRACKPAD</device_not>
    <autogen>__KeyToKey__
    KeyCode::F15, ModifierFlag::CONTROL_L | ModifierFlag::NONE,
    KeyCode::VK_CONSUMERKEY_MUSIC_NEXT
    </autogen>
    <autogen>__KeyToKey__
    KeyCode::F15, ModifierFlag::CONTROL_R | ModifierFlag::NONE,
    KeyCode::VK_CONSUMERKEY_MUSIC_NEXT
    </autogen>
  </item>

  <!-- Kinesis things -->
  <item>
    <name>Change Ctrl + Scroll Lock (power button) to Play/Pause on Kinesis</name>
    <identifier>private.asf.kinesis.ctrl-power.play</identifier>
    <device_only>DeviceVendor::KINESIS, DeviceProduct::KINESIS_ERGO_ELAN</device_only>
    <autogen>__KeyToKey__
    KeyCode::PC_POWER, ModifierFlag::CONTROL_L | ModifierFlag::NONE,
    KeyCode::VK_CONSUMERKEY_MUSIC_PLAY
    </autogen>
    <autogen>__KeyToKey__
    KeyCode::PC_POWER, ModifierFlag::CONTROL_R | ModifierFlag::NONE,
    KeyCode::VK_CONSUMERKEY_MUSIC_PLAY
    </autogen>
  </item>

  <item>
    <name>Change Help key to kp_enter on kinesis</name>
    <identifier>private.asf.kinesis.help.enter</identifier>
    <device_only>DeviceVendor::KINESIS, DeviceProduct::KINESIS_ERGO_ELAN</device_only>
    <autogen>__KeyToKey__
    KeyCode::HELP,
    KeyCode::ENTER
    </autogen>
  </item>
</root>