Replace SID to SERVICE_NAME in Oracle connnection string

I didn't test this against an Oracle environment, but the following should get you closer:

when CLIENT_ACCEPTED {
    TCP::collect
}
when CLIENT_DATA {
    set sid_match 0
    if { [TCP::payload] contains "CONNECT_DATA=" } {
        set sid_match 1
        log local0. "original payload = [TCP::payload]"
        set service_name "SERVICE_NAME=MYSERVICENAME"
        if { [regsub -all -nocase "SID=MYSID" [TCP::payload] "$service_name" newdata] } {
            TCP::payload replace 0 [TCP::payload length] ""
            TCP::payload replace 0 0 $newdata
            log local0. "replaced payload = $newdata"
        }
    }
    TCP::release   
    TCP::collect
}

You'll need to re-add your pool logic, but you shouldn't have to do any of the payload length manipulation. Output from test using an HTTP POST:

original payload = (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=10.11.110.10)(PORT=1521))(CONNECT_DATA=(SERVER=DEDICATED)(SID=MYSID)(CID=(PROGRAM=sqlplus)(HOST=xxxxxxx)(USER=xxxxxx))))
replaced payload = (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=10.11.110.10)(PORT=1521))(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=MYSERVICENAME)(CID=(PROGRAM=sqlplus)(HOST=xxxxxxx)(USER=xxxxxx))))