User-Agent Switcher for Chrome
More About User-Agent Switcher
The User-Agent Switcher for Chrome is the answer. With this extension, you can quickly and easily switch between user-agent strings. Also, you can set up specific URLs that you want to spoof every time.
Please note that this does not provide improved privacy while browsing the Internet and that some sites might have other means to figure out that the browser is not what it pretends to be. Running this extension can have performance impact on your browsing experience due to its need to intercept and modify the data communicated to the server.
NOTE: if some sites have problems after using a mobile user-agent, and won't switch back no matter what you spoof, you will need to switch the user-agent back to Chrome *and* clear your cookies for the sites to treat the browser normally again.