As of Identity Suite 14.2 vApp CP2 as well as Identity Suite 14.3 CP2, changes to the external DB details do not require a redeployment - as per the official documentation
https://techdocs.broadcom.com/content/broadcom/techdocs/us/en/ca-enterprise-software/layer7-identity-and-access-management/identity-suite/14-2/virtual-appliance/Change-the-Password-of-Identity-Suite-Components.html#concept.dita_6599601b-9f72-4020-924e-461f4ce8109c_ChangeDatabasePassword
for 14.3 CP2
https://techdocs.broadcom.com/content/broadcom/techdocs/us/en/ca-enterprise-software/layer7-identity-and-access-management/identity-suite/14-3/virtual-appliance/Change-the-Password-of-Identity-Suite-Components.html#concept.dita_6599601b-9f72-4020-924e-461f4ce8109c_ChangeDatabasePassword
for 14.4
For older releases, the following procedure is valid.
As a prerequisite, all the data should be manually migrated from the old DB to the new DB for all deployed applications.
Once done:
1. Login to the vApp Dashboard
2. Choose Setup from the top left Menu
3. Edit DB details and reference the new DB server
4. Redeploy with the updated details