The change you are looking to make could be handled simply by following these two steps:
1. Disconnect the active connection using console command -
F CCITCPGW,DISCONN,SYSTEST
- for SSL version:
F CCISSLGW,DISCONN,SYSTEST
2. Update the NODE definition using console command -
F ENF,NODE(TCPIPGW,SYSTEM.NEW.HOSTNAME.COM,,SYSTEST)
- for SSL version:
F ENF,NODE(TCPSSLGW,SYSTEM.NEW.HOSTNAME.COM,,SYSTEST)
These 2 commands should be all that is needed. Following the issuance of the NODE command, the connection should be eligible to be re-driven automatically.