Karl referenced correctly, but will explain bit more here.

If this is A->B and A->C (one to many), by reversing the replication on A->B, the new setup will become cascaded (B->A->C)

To convert to one to many to cascade, ensure first, nas_refresh -refresh works good from A->B and A->C and finishes with no issues. Once it is good, you can issue, nas_replicate -reverse from A to convert to cascaded.

Once you got like that above, you push the commonbase ckpt like Karl referenced, which you can do like:

1) Create B-C interconnects

2) Create the ckpt on B (the new source) -> fs_ckpt fsname -name fs_cb_ckpt

3) From B to A session ->  nas_replicate -refresh fs1_BtoA_rep -source fs_cb_ckpt -destination fs_cb_ckpt

4) Once above sync finishes, then issue on A -> nas_replicate -refresh fs1_AtoC_rep -source fs_cb_ckpt -destination fs_cb_ckpt

5) when the above finishes, you can delete the replications from A-C first

6) create new rep from B to C like (this will do the incremental copy) : nas_replicate -create fs1_BtoC -name sourcefs -destination destfs -vdm ifany -interconnect BtoC_interconnect -overwrite_destination

7) Delete B-A session