How do I convert a postgres 9.3 Slave to read-write without Impacting the Master

I have a Postgres 9.3 Master-Slave stream replication setup on Ubuntu.
I would like to just convert the Slave into read-write by breaking the replication. However, I do not want the Master to be impacted in any way, as its a critical Production. All I want is to have a clone of the Master, so that I can test pg_upgrade.

Can I just run a "pg_ctl promote" on the slave, and open the Slave for read/writes? Does running "pg_ctl promote" on the Slave have any impact on the Master?

Thanks very much.