using pgbackrest in a PG streaming replication cfg with repmgr

Hi List, 

We  have a requirement to start using pgbackrest for  db backups  on slave PG hosts already configured in Streaming Replication  .   To avoid any issues with WAL files  transfer and performance in  existing PG streaming replication configuration , we plan to run pgbackrest only at a slave host and only full database backups ( no need for PITR/incremental  when already have synchronous replication) . My questions are :

-How do I cfg pgbackrest to not archive/use WAL files  without affecting the synchronous  streaming replication?

- Are any known issues with pgbackrest + repmgr  when running : repmgr standby switchover  ?( to promote a new  db master while slave is online ) or repmgr promote ?

thank you !!!