switching replication from standard asynch to slots

I have a few production environments that use vanilla streaming
replication. (9.5 and 9.6)

I'm curious if I can create the replication slot on the primary host,
shutdown postgres on the secondary replica, update the recovery.conf to
include the primary_slot_name, and restart postgres on the replica to
effectively 'switch' over to use the slot for streaming without repriming
with a fresh pg_basebackup.

Also curious if I get into a pickle because of limits in pgsql_xlog disk
space if I can just shut down the replica, remove the slot information, and
do whatever cleanup is required on the primary and restart the replica with
the slot information removed from the recovery.conf and go back to vanilla
streaming replication without repriming.

Anyone do this kind of slot/streaming switcheroo?

Mike