Attempt to change Mongoose.js Discriminator Value tied mapping leaving Discriminator Name untouched

createReflectedDiscriminator.js

// https://github.com/Automattic/mongoose/issues/2596
// 1. It was necessary for me to to fit our naming style to this behaviour.
// 2. And moreover, move to Mongoose 5
// 3. And leave all data untouched, I mean, no changes, at all, a lot of production running data.

/**
 * Discriminator Reflected mapping
 * to discriminator value,
 * used inside of existent db
 * @param {object} baseModel           : parent model used for discriminator creation
 * @param {object} discriminatorSchema : shema to create discriminator from
 * @param {string} value {string}      : your existent Discriminator Key value!
 *                                       may be your former discriminator name
 *                                       at least 4 me it was so
 */
const createReflectedDiscriminator = (baseModel, discriminatorSchema, value) => {
	const parentModelName = baseModel.modelName || baseModel.name;
	const discriminatorModelName = `${parentModelName}.${value}`;
	const d = baseModel.discriminator(discriminatorModelName, discriminatorSchema);
	d.schema.discriminatorMapping.value = value;
	baseModel.discriminators[value] = d;
	const schema = baseModel.discriminators[value].schema;
	const key = schema.options.discriminatorKey;
	schema.remove(key);
	var obj = {};
	obj[key] = {
		default : value,
		select  : true,
		set     : function(newName) {
			if (newName === value) {
			  return value;
			}
			throw new Error('Can\'t set discriminator key "' + key + '"');
		},
		$skipDiscriminatorCheck : true
	};
	obj[key][schema.options.typeKey] = String;
	schema.add(obj);
	return d;
};

module.exports = createReflectedDiscriminator;

It is all about the topic from there
Discriminator Key is tied to Model Name #2596