AddCustomValidationSystemConfigurationField

requirejs-config.js

var config = {
    config: {
        mixins: {
            'mage/validation': {
                'MageVision_Blog48/js/system/config/validator-rules-mixin': true
            }
        }
    }
};

system.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
        xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
    <system>
        <tab id="magevision" translate="label" sortOrder="1000">
            <label>MageVision Blog Posts</label>
        </tab>
        <section id="blog48" translate="label" type="text" sortOrder="1010" showInDefault="1" showInWebsite="1" showInStore="1">
            <label>Post 48</label>
            <tab>magevision</tab>
            <resource>MageVision_Blog48::blog48_configuration</resource>
            <group id="post48" translate="label" type="text" sortOrder="10" showInDefault="1" showInWebsite="1" showInStore="1">
                <label>General</label>
                <field id="custom_validation" translate="label" type="text" sortOrder="10" showInDefault="1" showInWebsite="1" showInStore="1">
                    <label>Custom Validation Greater than 1</label>
                    <validate>validate-greater-than-one</validate>
                </field>
            </group>
        </section>
    </system>
</config>

validator-rules-mixin.js

define([
    'jquery'
], function ($) {
    'use strict';

    return function (target) {

        $.validator.addMethod(
            'validate-greater-than-one',
            function (value) {
                return !(value <= 1);
            },
            $.mage.__('Please enter a number 2 or greater in this field.')
        );

        return target;
    };
});