After BGP is established, changes to policy on routers take effect immediately but are not applied until an update is triggered. So ultimately, this must be done manually.
There are two methods for triggering an immediate update: hard and soft resets.
To perform a hard reset, which is disruptive and will drop BGP adjacency:
clear ip bgp *
To perform a soft reset for either inbound or outbound policy, observe the following. Note this is called route refresh.
clear ip bgp <neighbor IP> [in|out]
Stuck-in-Active: Journal of an IT-Network Administrator 