MacOS – Re-map keys on keyboard

Here's how you can get ⌃ Control+arrow keys to work like you describe. Copy the following property list into ~/Library/KeyBindings/DefaultKeyBinding.dict (you can create the directory if it doesn't already exist):

{
    "^\UF703" = ("moveWordForward:", "moveWordForward:", "moveWordBackward:");
    "^$\UF703" = ("moveWordForwardAndModifySelection:", "moveWordForwardAndModifySelection:", "moveWordBackwardAndModifySelection:");
}

This will set up ⌃ Control+arrow to navigate to the beginning of the next word (by using OS X's normal navigation three times: to the end of the current word, end of the next word, then back to the beginning of the next word). I also included a version that works with ⇧ Shift so you can select text as you go.

Caveat: this will only work in Cocoa apps, but I think the normal ⌥ Option+arrow navigation does too. Also, make sure to relaunch your apps!

@iGameRam's suggestion of KeyRemap4MacBook ended up working for me. I selected KeyRemap4MacBook because I am already using it to remap keys for me system wide. To do this I had to read the reference manual.

From the reference manual I found that there is a private.xml file that enables me to add more remapping values to KeyRemap4MacBook. By going to the KeyRemap4MacBook pref pane, going to the "Misc & Uninstall" tab and selecting "Open private.xml" I was able to open the file.

I had to add two elements to my private.xml. The first was:

<appdef>
  <appname>SPOTIFY</appname>
  <equal>com.spotify.client</equal>
</appdef>

This is because KeyRemap4MacBook does not ship with an app definition for Spotify. It does ship with many others. I need the app definition so my keyboard keybindings only apply for Spotify and are not system wide.

The second element I added was:

<item>
  <name>Spotify Vim Style Nav</name>
  <appendix>J and K works in Spotify</appendix>
  <identifier>private.spotify.vim_style_nav</identifier>
  <only>SPOTIFY</only>
  <autogen>--KeyToKey-- KeyCode::J, KeyCode::CURSOR_DOWN</autogen>
  <autogen>--KeyToKey-- KeyCode::K, KeyCode::CURSOR_UP</autogen>
</item>

This is the actual definition of the key bindings. The <identifier> tag is supposed to be unique for every key mapping. The manual suggests prefixing the identifier with private.. The <only> tag has to match an appname defined in the private.xml or shipped with KeyRemap4MacBook.

The <autogen> tags are supposed to contain the mappings. The manual has many examples on what kind of mappings that can be created. The two I have map the J and K keys to the Down and Up keys respectively.

Once the file has been saved, I just needed to press the "ReloadXML" button and then my mapping appeared as an option in the menu.

After selecting it everything worked as I wanted.