A lot of people are wondering how to prestage DFS-R, so here are the steps:
Make sure that the primary member has the latest version of each file. This is done during configuration of replication because it will be seen as authoritative during first replication. This is similar as doing a D2/D4 restore of a broken sysvol.
During first replication these things will happen:
[P1 = Primary]
[M1 = Member]
File1 exists on both P1 and M1 and are identical = File is not replicated, but metadata is to update the replication DB on M1.
File2 exists on both P1 and M1, but is newer on P1 = File2 will be replicated, and the file on M1 will be treated as a conflict and moved to a special folder called something like "conflict or deleted"
File3 does not exist on P1, but gets created on M1 during first replication = File3 will replicate to P1.
File4 exist on both P1 and M1, but gets deleted during first replication = The deletion doesn't replicate.