To use both DFS and FRS replication with DFS replication being the primary replication method, you can run the following command:
dfsrmig /setglobalstate 1
This command sets the global migration state to "Prepared" which allows you to configure DFS Replication to be the primary replication method. After running this command, you can use the DFS Management console to configure DFS Replication and initiate the staged migration from FRS to DFS Replication