Can't use non-numeric string as operand of "&&" in rule

Depends on to what the elseif is attached. Does it apply only when one of the three URI paths are matched? If not, you could place a return in the existing match clause, then put your if...else outside the switch, like so:

when HTTP_REQUEST {
    switch [HTTP::uri] {
        "/extern/test.jsp" -
        "/SO/services/dat" -
        "/Ex/services/pay" {
            if { !$renegtried && [SSL::cert count] == 0 } {
                log local0. "[IP::client_addr]:[TCP::client_port]: A log entry"
                HTTP::collect
                SSL::cert mode request
                SSL::renegotiate
                return
            }
        }
    }

     end up here if none of the three URI paths above match, or if one of them does match
     but either $renegtried or SSL::cert count != 0
    if { [string tolower [HTTP::host]] equals "www.test.es" } {
        pool SECOND_POOL_SSL
        SSL::enable serverside
        log local0. "WITH SECOND POOL"
    } else {
        pool THIRD-POOL-SSL
        SSL::disable serverside
        log local0. "WITH THIRD POOL POOL"
    }
}

For test of HTTP::host using string tolower is important, because the client may submit the Host: header in any case, and DNS is case indifferent.