I wouldn't violate the centerline rule, even if it seemed "okay". There's a reason for it, and it's all about the racer staying healthy.
Also it's just easier following the rules. Violating the yellow line is like violating the Jr gear limit when there is no rollout. If someone (not an official) says they're not enforcing rollout, and you verify that there is, in fact, no rollout area, what would you do? I kept my 53x15 on, my teammate slapped on a 12. I think the first 8 or 10 finishers at the race were disqualified when they failed rollout (set up during the race), including my teammate. And he had the gaul to be mad about being DQed.
cdr