I’d advise you try it out at Starbucks first (if your Starbucks takes names), or go to a store where they ask your name & write it on the fitting room door. Sometimes names seem great in theory, and sometimes they’ll make you feel awkward when you have to admit it’s your name.
I know a girl named [name]Emerald[/name], and I felt awkward calling her that, but it did suit her. She was an ‘old time Hollywood Glam’ type in looks and very charismatic. If I’d grown up with her, I’m sure I’d see it as a ‘normal’ name, though.
If you’re set on it, go for it. I mean, why not? If everyone calls you “[name]Em[/name]”, though… why change your name for distinction from the other Emilys when you’d still get called [name]Em[/name]? You could just tell the people who call you [name]Emily[/name] to call you [name]Em[/name] instead. I think that’ll me a much easier transition than getting them to call you [name]Emerald[/name], y’know?
I think if you chose the name [name]Emerald[/name]… I’d kind of get an attention-seeking vibe. Either that, or I’d expect you to at least be hipster-y, or super, super outgoing.
An other way to test [name]Emerald[/name] out is to change your name on facebook and see how people react. I unofficially changed my name when I was 19 after having the nickname [name]Lucy[/name] for 10 years already at that point. This past year I changed my name on facebook from my legal name (which is what my coworkers all know me as, and anyone I met during or after university. Everyone I knew in high school or before knows I’ve preferred [name]Lucy[/name] since grade 5). Changing it on facebook for a fair amount of comments, but I just explained my history and everyone was super accepting of it.
If you change it on facebook, even if people assume it’s a joke, they may have an easier time putting [name]Emerald[/name] in to practice after seeing the name next to your picture.
(oh, and an other option could be [name]Emilia[/name]. Since a friend already calls you [name]Amelia[/name], this could be a simple transition, too)