FYI.
I tried the 'replace pattern' command; the result is below.
root@SRX1500-cluster# replace pattern reth0 with reth4
error: target statement 'reth4' already exists
[edit interfaces]
'reth0'
could not rename to 'reth4'
Thus, I ran 'replace patterh reth0 with reth10' and then configured the 1 Gbps links to have reth10 as their redundant parent. Lastly, I changed the redundant parent of the 10 Gbps to be reth0, as you recommended.