Applying Multiple SNATs on an Outbound Virtual Server

Try this

  
  when CLIENT_ACCEPTED {  
      switch [IP::client_addr] {  
        10.10.10.1 { snat 100.100.100.1 }  
        10.10.10.2 { snat 100.100.100.2 }  
        default { forward }  
      }  
  }  
  

I haven't tested this, but I think this is a good start from an iRule perspective.

You can also take a look at the "Configuration_Guide_for_BIG-IP_Local_Traffic_Management_9.3.0.pdf". Chapter 13 does provide you a way to create a Pool of snat address and perform a one to one mappings. Then you need to apply it to the vip, thereby, avoiding using an irule.