Poiicy based virtual server

I assume you mean a Local Traffic Policy? If so, in the "forward" target, you can add an target action using the parameters "snat" or "snatpool" an the same time as you add a pool target.

If you want to use an iRule, you can simply add the "snat" command to the portion of your iRule logic that does the pool selection. The argument to the "snat" command is either "automap", a pool name, or "none".

Here is an example of a Local Traffic Policy that would do a selective SNAT.

ltm policy multi-snat-test {
    controls { forwarding }
    requires { http }
    rules {
        rule1 {
            actions {
                0 {
                    forward
                    select
                    snatpool /Common/SNATPOOL
                }
                1 {
                    forward
                    select
                    pool THEPOOL
                }
            }
            conditions {
                0 {
                    http-uri
                    values { /path1 }
                }
            }
            ordinal 1
        }
    }
    strategy first-match
}