Locale nlLocale = new Locale("nl", "NL");
NumberFormat.getCurrencyInstance(new Locale("nl", "NL")).setFormatPattern("€ #");
Leaving aside the question of whether that particular format is "correct" or not, the way to change the currency instance for the "nl" locale is to implement and configure a custom
LocaleServiceProvider for the number format service. (The provider class needs to subclass
NumberFormatProvider, but the superclass javadoc explains how to configure the provider.)
The provider needs to return a non-standard
NumberFormat instance for the particular case you are concerned about, but (presumably) delegate to the default provider in other cases.