Well, smiling can make you happy even if your aren't feeling it when you start smiling. I have often used, and do occasionally still use this technique when I'm feeling down. Force a smile. Hold it. Feel cynical about it, doesn't matter. (I used to repeat sarcastically: "Nothing bad ever happens to me" while I waited.) After a minute or two, the smile begins to change from a forced smile to a real smile. And then you're feeling good. Brain and body -- it's a two-way street. So yeah, go ahead and smile. You'll be happier for it!
Sure. After two decades of faking it to no avail, people're gonna tell me to fake it some more. Maybe I just didn't hold the grin long enough or something. If short-term joy is your definition of happiness - sure, go for it. Not sure if it fixes the heap of unaddressed problems one's sure to accumulate by not pretending to be... "happy".