I was asked for a quick sample of how to build a culture, so here it is: 

1.) Start an elevated command prompt (have to be elevated to run CultureAndRegionInfoBuilder.Register())  (press windows key, type cmd, press ctrl+shift+enter is one way).
2.) copy the code below to testcc.cs.  (notepad testcc.cs and cut & paste the code).
3.) in cmd, add .net to your path:  path=%path%;%windir%\Microsoft.NET\Framework\v4.0.30319  (Please use Microsoft.Net Framework v4 (or whatever's later if you read this in the future), it has more fields)
4.) csc /r:sysglobl.dll "testcc.cs"
5.) testcc.exe
 
You'll have to restart any managed process using the symbol, but intl.cpl should show you the updated results.
 
This makes an et-EE.nls file in %windir%\globalization, and a registry entry.  See http://blogs.msdn.com/b/shawnste/archive/2009/05/14/cheating-to-uninstall-custom-cultures-locales.aspx for how it might be pushed with an admin logon script.  You can remove the "Register" statement, recompile & rerun to remove it.
Remember all the "AS-IS, no warranty, I didn't bother to test it" stuff that's in the Terms of Use :)
-Shawn

// testcc.cs

using System;
using System.Globalization;

class Test
{
    static void Main()
    {
        // Show what we were
        Console.WriteLine("Old Currency Symbol: " + new CultureInfo("et-EE").NumberFormat.CurrencySymbol);
        Console.WriteLine("Old Currency Name: " + new RegionInfo("et-EE").CurrencyEnglishName);
        // Build new one
        CultureAndRegionInfoBuilder updated = new CultureAndRegionInfoBuilder("et-EE", CultureAndRegionModifiers.Replacement);
        updated.CurrencyEnglishName = "Euro";
        updated.CurrencyNativeName = "Euro";
        updated.ISOCurrencySymbol = "EUR";
        NumberFormatInfo format = updated.NumberFormat;
        format.CurrencySymbol = "€";
        updated.NumberFormat = format;
        // Get rid of anything there used to be
        try
        {
            // See if there's an old one to obliterate
            CultureAndRegionInfoBuilder.Unregister("et-EE");
        }
        catch
        {
            // Should worry about errors, I'm just assuming not registered.
        }
        // Register it
        updated.Register();
        // Have to re-run to show the new values
    }
}