I too face a similar issue. I would like to update AFM address lists via iRule but sadly I don't think it's possible. I made a post about it here on the forums a while back and one of the F5 guys commented saying that he thought the use case was valid and that engineering should look into it but I haven't seen much.
What I started to do though was generate the commands for adding/editing AFM lists in powershell and using PoshSSH to connect and run the commands.
the tmsh command is something like
modify /security firewall address-list address-lists add {ip or addresslist i think}