Can I Change Datasources Without Restarting Applications Dependent on It?

No.  For instance, the current implementation of the CMP2 layer caches DataSource references.

-

Use a DataSource Delegator from varia. It is a service that implements DataSource but delegates

calls to some other DataSource. It is configured with managed attributes so you can change the

target DataSource at runtime w/o redeploying the app.

4.0+

See the ha jca connectors JBossJCADatabaseFailover for 4.0.x and latter.