NW will not be able to handle the exact same data with the same ssid's in two locations. So the original location should be down or made unavailable to do anything with it. But instead of performing mtree replication, so outside of the knowledge of NW, why not have NW control the replication, using cloning, or what is called CCR, clone-controlled replication, in case of DD's being involved as source and target as then the replication takes place between the DD's to replicate data in deduped format instead of having to fully read the data from one DD and write it to the other. So that way NW would be aware of the clone(s) existing and any of them could be separately from each other be used to restore data from. It is definitely the preferred way to replicate backup data with NW, so that it is aware of an replicas.

So by setting up a workflow using a protection group with the action type of "clone" that queries for the savesets to be cloned. Or do this via a script via CLI.

Having NW being in control also makes sure that only backup data that is actually completed is done, whereas with mtree replication you might never know what the actual state any replicated data would be in, as one would not easily be able to test and validate it, as the remote device would have to be scanned in, which it cannot do, as it would have a conflict with two times exactly the same data and ssid...

So please, make your life easier and use NW CCR...

https://www.dell.com/support/manuals/en-us/networker/nw_p_ddboostdedup_integration/ccr-format?guid=guid-ad132cdc-b544-45b2-81c4-91321a0400fa&lang=en-us

https://www.dell.com/support/manuals/en-us/networker/nw_p_ddboostdedup_integration/configuring-the-data-domain-ccr-environment?guid=guid-4fe43db7-c3bb-4582-bf0d-3627163c91cd&lang=en-us

NetWorker: Guide to Stream Usage with NetWorker 19 using Automated Multi-Streaming with Data Domain Clone Controlled Replication :

https://www.dell.com/support/kbdoc/en-us/000181762?lang=en