Add a "set" command that can set and unset values like "start" does without doing anything else (clearing the tracer).

For example, to set the option "irq-info", simply do:

 # trace-cmd set -O irq-info

Or to turn it off:

 # trace-cmd set -O noirq-info

Basically, it will do any command that trace-cmd start can do, but without resetting or modifying anything else. Even let it change the current tracer or enable or disable events:

 # trace-cmd set -p function

Will be just like: echo function > /sys/kernel/tracing/current_tracer

Enable an event:

 # trace-cmd set -e sched_switch

Or disable an event:

 # trace-cmd set -v -e sched_switch

Allow it to take multiple arguments to do things in the order that they are.