If you want to add new custom configuration option to editor global variable than you need to below steps:

1. First you need to add your configuration option in your extension system.xml file.

<?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>
 <section id="general">
 <group id="store_information">
 <field id="company_no" translate="label" type="text" sortOrder="65" showInDefault="1" showInWebsite="1" showInStore="1">
 <label>Company Number</label>
 </field>
 </group>
 </section>
 </system>
</config>

2. After add configuration option you need to register your configuration option in Magento Variables via your di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
 <type name="MagentoVariableModelSourceVariables">
 <arguments>
 <argument name="configPaths" xsi:type="array"> 
 <item name="general/store_information" xsi:type="array">
 <item name="general/store_information/company_no" xsi:type="string">1</item>
 </item>
 </argument>
 </arguments>
 </type>
</config>