Which document are you using to prepare for this task? I think the requirement means that all four systems should be on the same cluster switch, not that you must use e0a on all of the nodes, but I admit I could be wrong on that one. I have reviewed this document and can not see it in there
Has a cluster switch been made available for the process?
In relation to your question, no, my understanding is that on the A400, those ports cannot be used for cluster interconnect at any time.
I vaguely remember similar problem I had during ARL head swap. Old and new head had different Ethernet ports, and after head swap new node inherits configuration of old head so it had no working cluster ports. I had to manually adjust configuration before node could join the cluster, but I do not remember how.
For next head swap with this customer I configured cluster ports in advance to ensure there was some overlap so at least one working cluster port was available after head swap.
The below guide can be used to upgrade controllers of different platforms even though the versions and specific platforms you mentioned are not the same, but the process is essentially the same. Specifically, page 8 discusses preparing the ports of the new controller for the Cluster LIF.