Grok expressions don't need to contain grok patterns like COMBINEDAPACHELOG. In the end it just gets expanded to a normal regular expression anyway. See https://www.elastic.co/guide/en/logstash/current/plugins-filters-grok.html#_regular_expressions.
If you want to define your own grok patterns that you can reuse. See https://www.elastic.co/guide/en/logstash/current/plugins-filters-grok.html#_custom_patterns.