Remapping Alt + F2 in Unity

Solution 1:

Install gconf-editor if you don't have it. sudo apt-get install gconf-editor
Under Apps-compiz-1-plugins-unityshell-screen0-options set execute command to whatever you want it remapped to be.

One example could be Alt. If you want to set it to something that is already occupied(in the case of this example Alt, you may need to unset that shortcut in keyboard shortcuts first).

Reports indicate that setting it to nothing is ineffective. I would recommend setting it to something you don't anticipate using.

Solution 2:

This is how I managed to do this with Unity

• Install CompizConfig by execute

  sudo apt-get install compizconfig-settings-manager

• Open CompizConfig by typing "compiz" into your launcher or ccsm in terminal.

• Choose Advanced search, enter execute a command into the search box, choose Ubuntu Unity Plugin on the right.

• Edit the shortcut into something else, like Alt F3 and voila!

Credit: https://askubuntu.com/a/323945/189124