Currently the external editor supports XEmacs, VIM, and two
user-defined editor types USR1 and USR2. This style is inconsistent
with other NetBeans configuration UI and does not take advantage of
the Services API.

Proper style is to (1) define an abstract class e.g.
ExternalEditorType extends Object implements Cloneable, Serializable,
with some method(s) to initiate a connection and so on; (2) each EET
subclass (XEmacs + VIM perhaps) contains bean properties such as
command, host/port/password, XEmacs library location, whatever is
appropriate; (3) default instances of available EET subclasses are
placed in Services/ExternalEditorType/ in the layer using .settings
files with appropriate localized names and icons; (4)
UI/Services/.../Editing/ contains a .shadow file pointing to
Services/ExternalEditorType so it appears in the Options dialog;
Templates/Services/ExternalEditorType/ contains templates (.settings
with template=true file attr) for each kind of external editor so that
the user could create more of them, e.g. alternate XEmacs
configurations; (5) the main system option selects the external editor
type according to a property editor of type Object constrained to load
only ExternalEditorType, as described in the Services API "Property
Editor for Services", and saving the selection as a lookup ID.

You might have a generic EET subclass "unknown external process"
applicable to VIM and so on, with an arbitrary number of preconfigured
instances in Services/ but perhaps only one template in
Templates/Services/, which would launch a configurable process but not
provide any further UI to the user; use methodvalue="" in your
.settings to employ static factories to preconfigure several standard
instances of one class. This is as opposed to the XEmacs type which
permits the library location to be configured and so must be a
subclass.

An additional advantage of the services style is that if
ExternalEditorType is public and maintained compatibly, additional
modules could provide support for other editor types if they require
special setup beyond making a connection.