If you private a chest, and you change your name, you won't be able to access the chest.

You best hope, is to ask a mod to remove the sign, or change you name back.
Personally, I think asking a mod to remove it is better, though mods aren't always on 24/7.

I hope this helps.

Forum Name Change --> Important! - Forum changes | Skyblock Forums

 

Blaq already made a thread informing people of name changes.