You are designing a setup where the FortiGate device is connected to two upstream ISPs...

The soft reconfigure is correct by elimination (FGTs all support BGP Refresh, so question is not worded correctly - to refresh routes in advertisements, there is no need to do manually anything, after the change is committed to config FGT will send BGP Refresh message to the peers to notify them of it. The same is true for Cisco and Juniper routers. The question should ask "when routing policy was changed" - then yes, reconfiguraiton is the way to notify BGP peers that BGP policy was changed.