Seriously bad idea. You're going to disrupt someone's wedding and piss off the pro who is doing the actual wedding shoot; not to mention the fact that no one is likely to pose for you so you will be trying to steal every shot.
The correct way to gain experience is to offer your services to local wedding shooters as a second shooter. That way you don't upset anyone and you get to actually learn from the pro.
This is the best way to get in. and next to the pro, you will piss of the b&g too...unless you want pics of a shoe moving towards you 
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