public liability insurance? that doesnt sound good
If you don't understand let me explain, it's cover for the manufacturer, to protect them should one of their products fail.
Because they would be altering a product made by someone else, which is possibly already quite a long way through it's working life, which is an important safety item the insurance would be very expensive.
If it was a business operating without public liability insurance they would be open to huge claims, if one of their products failed, especially if injury or death was caused.
You'd be best off finding a mate who's prepared to do the work for you, although they'd need to be a very skilled mate, who'd be prepared to take a big personal risk.