IP Address Exception in ASM

As far as I'm aware, the closest option in GUI you have is creating an IP address exception (linked to a particular ASM policy). If you want something more granular (an exception, linked to a specific signature ID), it can be done using iRules only.

A single IP and signature:

when ASM_REQUEST_DONE {

  if { ([IP::client_addr] == "My-IP-Address") && ( [ASM::violation details] contains "My-Signature-ID") }{
    ASM::unblock
    log local0. "[ASM::violation_data]. Unblocked for [IP::client_addr]"
  }

}

Multiple IP addresses and multiple signatures:

when ASM_REQUEST_DONE {

  if { ( [class match[IP::client_addr] == "data-group-ip-address-list"] ) && ( [class match[ASM::violation details] contains "data-group-signature-ids"] ) }{
    log local0. "[ASM::violation_data]. Unblocked for [IP::client_addr]"
    ASM::unblock
  }

}