I'm wondering if there's a method to alter the database at runtime in grails - e.g., in many commercial/opensource Content management systems, they permit the database server to become located elsewhere, and you will specify the address in certain config screen at runtime.

since grails configs the database server using DataSource.groovy, how do you access the internals of the, and alter the database url? or database type even?

See Databases and Conditions within the Grails documentation.

Also see Externalized Configuration when the above does not completely suit your needs.

Grails does not care in which the DB resides as lengthy because it is accessible via JDBC, so getting the DB server elsewhere is not an issue, only a configuration.