Irule for Destination IP address and SNAT.

You should be able to use the code shown here as a base for what you are trying to do:

https://devcentral.f5.com/questions/how-to-use-irule-to-create-snat-based-on-destination-ip-address

Keep in mind that if you are making more than one or two comparisons, you would do well to use the 'switch' statement.