"...If you're "present" while..." Whether you're there or not doesn't matter. If a business does it, said business must have a firearms business licence and any employee who handles firearms must have a PAL for the class of firearm handled. It's like a the guy who sweeps the floor in a mechanic's shop being required to have a driver's licence. Daft.
Being present means you are "supervising" the handling of the firearm, which means no PAL is required. In any case, the application of logic would immediately produce the answer. Painting your firearms is legal, and even if it weren't the law is ridiculous and therefore only followed by those who fear their government.
TDC