Looks like the control only offers Hexadecimal, DecimalPlaces, and
ThousandsSeparator properties to control the format, not custom
formats.
You can probably subclass the control, add a Format property, and
override the UpdateEditText method to support a custom format like you
want.
However, since the ParseEditText property is not declared as
overridable, you can not add the logic needed to parse a totally
custom format--the format must be compatible with the default
Decimal.Parse() method.
If you do need an incompatible format, then I think the only option is
to create an entirely new NumericUpDown control that inherits
UpDownBase. It's a shame that so many of the windows controls methods
are not declared overridable--makes extending them difficult.
HTH,
Sam