As long as you have high faction, you can decline multiple missions. You take a -0.001 hit to faction so as long as its high like 7 or 8 modified you should be good. Do your pirate arcs
Be mindful though to the agent standing that it doesnt drop too much.
Ah pirate burners. Train crim connections to 5 and do your arc. Depending on the pirate faction, you can raise or pay to have raised, the corp that gives access to the arc. Ex ytiri at 3.00 will let you run the pirate arc
Tbh im not totally sure on the reduction for pirate factions. We typically dont do pirate missions. Once faction drops below 5.00 modified, you cant run any corp unless you have high enough standings