Let's see if I understand the request:
The posted configuration has a current existing layer 3 /30 routed link on this interface untagged facing switch A
The desire is to add a second VLAN layer 2 only tagged to the same interface.
the same VLAN will then be added to a similar interface with a similar configuration facing the second switch B.
the desire is that this VLAN exists then layer 2 connected between switch A and B via these SRX ports.