Mr Flufferpants - while cute - doesn't have much ring does it? I couldn't imagine having to call it out at the park to get my Dog to come back LOL LOL
Dixie responds to half a dozen names because I'm always calling her something different. There's Dixie, Dougal (Yes, she responds to Dougal - I'm trying to untrain that one!), Little, Wee, Evil Wee, Lil Butt, WeebaLow, Dixel-berries. Yes I know it's probably bad obedience to use so many names but she does come to just about anything! LOL!
And when I want to call them both back I use "Yorkies!" or "york-a-lorks", or even some words which I won't post because they're rude! But it works.
So I guess my advice is - just go for it. Try treating a lot and saying the dog's new name, use the name whenever you pat the dog or cuddle the dog and he'll soon come to associate the name with good things!