Here is two solution
1) add below file default.xml in one of your module
<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<body>
<referenceBlock name="privacy-policy-link">
<arguments>
<argument name="label" xsi:type="string">Custom Privacy and Cookie Policy</argument>
<argument name="path" xsi:type="string">privacy-policy-cookie-restriction-mode</argument>
</arguments>
</referenceBlock>
</body>
</page>
2) Create a theme add below file
app/design/frontend/vendor/mytheme/Magento_Theme/layout/default.xml
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<body>
<referenceBlock name="privacy-policy-link">
<arguments>
<argument name="label" xsi:type="string">Custom Privacy and Cookie Policy</argument>
<argument name="path" xsi:type="string">privacy-policy-cookie-restriction-mode</argument>
</arguments>
</referenceBlock>
</body>
</page>