It wont hurt your sales, people will just look at your feedback if they wonder why you changed it.
I had 5 numbers and a full stop at the end of mine, it was confusing, so a few months ago i changed the end of it to 3 simple numbers i could remember, it was an easy process.
Not sure about the old customers, but if they have you in their fav sellers you will still remain there.
What you could do is change it back and have your old one in brackets after it, leave it for a few months then change it.
I recon just go for it