On my remote I can hit the "+" "-" buttons to change TV channels on the fly - but sometimes it causes the picture to freeze (going from SD to HD and vise-versa). I found that it is the RO+HQ setting (using MadVR) that is causing the issue. I then setup Custom Video Mode to use EVR for TV Viewing. Note that this freezing issue may have been fixed in .201+, I haven't retested. But it takes MC 4 or 5 seconds to start playing a new channel so switching back and forth to skip TV commercials doesn't offer much of an experience except 10 seconds of silence.
EDIT: Sorry I didn't understand/read your question (title) completely, your asking about a "previous channel" button, not switching channels on the fly.