The changes you assign here will be detected by clients when they contact the Notification Server to check for an updated configuration. By default, this happens every 60 minutes. If it finds that the configuration it holds is different than the one being offered by the Notification Server, it will download the updated configuration and begin using it.
Reinstalling the agent is necessary only if the agent has some sort of problem (error message, misbehaving, etc). An installation procedure also happens when upgrading to a new agent, such as after updating your Notification Server to a new version. If your NS is SP5 and your clients SP4, for example, you should enable an upgrade policy on your NS so that your clients will run the upgrade installation procedure.
Does this help?