There isn’t a way to skip them currently. The existing theory is that changelog-level preconditions are evaluated before any changeSets are executed, and the set of preconditions is the union of all the preconditions in all the changeLogs.
There is a feature in jira to support what you are wanting, but it is not in right now.
You can have changeSet-level preconditions of , but it would need to be set on each changeSet in your changeLog.
You could write a custom changelog parser (liquibase.org/extensions) to build in whatever logic you need to build up the changelog to run, but that may or may not be too much work for you.