Class C Airspace. Sorry to dissapoint.
I don't usually separate VFR from VFR. But, with class C being controlled airspace, and me being the controller, I do provide extra protection for Aerobatics and Parachute Ops etc..
Regardless of the Airspace Category and VFR requirments, I don't think it very wise to fly through (or allow an aircraft to fly through) an area of (Controlled) Airspace that has aerobatics in progress.
Also, an unverified Mode C is not necessariy wrong, it is just as it sounds - Not verified as being correct on this flight at this time. If a mode C is discovered as being outside of it's limits in flight, the pilot is requested to turn off mode C. It's nothing to do with equipment calibration.
Altimiters are calibrated on every flight prior to departure - what does the pilot do with the QNH?