Is there a way to define queuing discipline (FIFO etc) for a service?
The default for a service is FIFO, the other option is to use priorities:
This is the same as priority based in the queue.
To do a LIFO you can do it using priorities, setting up the priority as the time in which the agent arrived to the queue. The bigger the time, the best priority it has.
To do an agent comparison, you can also manage to do that only with priorities.
Conclusion: even if there's no explicit way to define the queuing discipline as you call it, you can still do it accepting the default fifo or using the priorities depending on your needs.