If I add the following to
router bgp 65004
adding this>>> network 10.1.23.0 mask 255.255.255.0
Will it cause any notwork disruption or cause BGP to re-converge?
It shouldn't cause your BGP sessions to reestablish or reconverge. It should only cause BGP to begin announcing 10.1.23.0/24 to BGP peers as long as this route is in your route-table learned from an IGP or as a connected or static route. 'show ip bgp' will reveal if it's in the bgp table.