pool set in irule overidden by httpclass

You could use the HTTP::class disable command to prevent HTTP class matching from happening, and event disable to prevent any further iRules from firing; you could also specify the HTTP_REQUEST event with that last command to prevent only that event from proceeding further. Note that both of those commands operate on a per-connection basis, not per-request. If you wanted the next HTTP request on the same connection to be treated normally, then you'd need to reenable both of those later in the transaction, perhaps in HTTP_RESPONSE.