It would be nice if the run mode support in both the JCR installer (https://sling.apache.org/documentation/bundles/jcr-installer-provider.html#runmode-support) as well as the File installer (https://sling.apache.org/documentation/bundles/file-installer-provider.html#runmode-support) would be enhanced so that apart from the AND logic (with ".", requiring all run modes to be active) also an OR logic would be supported (i.e. to set a certain config on an instance having runmode a or b) without being forced to duplicate that config.
As a syntax one could choose to use "|" as OR separator and keep using "." as AND separator (similar to the syntax of https://sling.apache.org/documentation/bundles/sling-settings-org-apache-sling-settings.html#defining-valid-run-modes). OR should have higher precedence so that AND is processed last.