Combining Two irules as one irule

You can try this by creating 2 datagroups - CLASS_NETWORK with 12.x network and CLASS_DOMAIN_POOL that has the domain name as the "key" and the corresponding pool as the "value":

when CLIENT_ACCEPTED {
set DEFAULT [LB::server pool]
}

when HTTP_REQUEST {

if { ([HTTP::uri] contains "/something") } {
    if { ([class match [IP::client_addr] equals CLASS_Network]) } {
        pool something_http_pool
    } else {
        log local0. "_discard_something"
        discard
    }

} elseif { [class match [HTTP::host] eq CLASS_DOMAIN_POOL] } {
     set POOL_SELECTED [class match -value [HTTP::host] contains CLASS_DOMAIN_POOL] 
     pool $POOL_SELECTED

} else {
    pool $DEFAULT
} 
}

I have never used "switch" within an if-statement but you can try to see if this will work by using "switch" within the "else" :

when HTTP_REQUEST {

if { ([HTTP::uri] contains "/something") } {
    if { ([class match [IP::client_addr] equals CLASS_Network]) } {
        pool something_http_pool
    } else {
        log local0. "_discard_something"
        discard
    }

} else {
  switch [HTTP::host] {
    "http-abc.xyz.com" { pool http_api_abc_test_pool }
    "webportal-abc.xyz.com" { pool webportal_abc_test_pool }
    "abc.xyz.com" { pool abc_test_pool }
    "two-abc.xyz.com" { pool two_way_abc_test_pool }
    "xml-api-abc.xyz.com" { pool xml_abc_test_pool } 
    "smpp-abc.xyz.com" { pool smpp_abc_test_pool }
   }
}
}