You can register as many plugins as you wish. As long as you add the fully qualified file name to a file in
resources/META-INF/services/net.corda.core.node.CordaPluginRegistry it will be loaded by the service loader and registered as a plugin in the node.
If you have created a project from the template CorDapp then you can simply add it to the existing services file that will be in
kotlin/src/main/resources/META-INF/services/net.corda.core.node.CordaPluginRegistry. The fully qualified class names have to be on separate lines.
You can read more about the plugin system here.