All hotkeys can be changed. Simply go to the chrome extensions tab (get there by either entering "chrome://extensions" in the URL bar or from Chrome menu -> tools -> extensions). At the bottom there is a button for "Keboard Shortcuts" where you can change the hotkeys to those of your choosing. In this menu you can also set the hotkeys to be global across either Chrome or your system.
Once Streamkeys is installed you will see an "sk" icon in your browser window next to the URL bar (and any other extension icons that you may have installed). Clicking on this icon will open up the extension popup window. The extension icon color will be green if the tab you are on is a music site and Streamkeys is connected to it. The extension icon color will be grey if the tab you are on is either not a supported music site or a music site that is currently disabled. From the popup window inside a music player tab you can enable and disable support for either the current music site (across all tabs) or just the current tab.
On the options page you can enable/disable Streamkeys for any site. You can get to the options page from either the Chrome extensions tab (chrome://extensions) or from the Streamkeys popup window. This page is useful if you have multiple different media sites open, and want Streamkeys to ignore any number of them.
To remove Streamkeys (or any other Chrome extension) go to the Chrome extensions tab (chrome://extensions) and click the trash icon next to the Streamkeys listing.
Play/Pause: Media Key Play
Next Song: Media Key Next
Previous Song: Media Key Previous
Mute: Ctrl+Shift+2