That's for the three engine rule. And yes, the head can be removed all you want, it's the back plate that Nova puts paint on the bolts to see if they have been removed. Again, this is Nova doing this, not IFMAR.
I was not at this race but in 2003 they tore down the top few finishers motors for inspection after the main. I seriously doubt Nova is going to give one of their drivers a hard time right after he finished at the top in the final. Especially since the Nova folks were there in person.