WAL Async Replication Question

List,

I've done WAL async replication between two Postgre servers in Pirmary
and Standby node as a test bed on two Virtual Machines on CentOS 8.
Postgres12.

Now I want to do the same WAL replication on a Production Postgres
server to a new standby server.

Is there a way to do configurations for WAL async replication on primary
server without affecting the customers / applications that depend on this
primary DB server?

As it is a production server, any changes we make to configuration files
may affect the services right ? or what unseen problems can arise in this
use case?

How to minimize the downtime / without service interruptions from the
Primary server while doing WAL replication to a Standby server.

Any hints / directions most welcome .. How will geeks do this in this
situation?

Yours,
Krishane