Unregister file

Hi,
I'm writing a little extension for mozilla. In a previous version a 
register locale information with a line like:

registerChrome(LOCALE | DELAYED_CHROME, regfldr, 'locale');

then, in the latest version, a register more locale:

registerChrome(LOCALE | DELAYED_CHROME, regfldr, 'locale/en-US');
registerChrome(LOCALE | DELAYED_CHROME, regfldr, 'locale/it-IT');
....

the problem is that if a user had previusly installed an old version in 
installed-chrome.txt I see both the new registration and the old one. 
But, in chrome.rdf, I see only the old registration information. There's 
a way to unregister and old locale and the register a new one?

Thanks,
Lithian.