Boeing sometimes puts some extreme maneuvers into the approved flight test card, which is performed with FAA approval.

There has been several cases of 737s being rolled (accidentally) without damaging the airframe.

When test pilots fly extreme maneuvers on an approved test profile, its usually done at high altitude, not airshow flyover altitude.

Before the famous 787 demo flight, the pilot flew the maneuvers in a simulator, and did some practice at higher altitude before doing a low altitude demo routine.

At Boeing, there's a fine line between selling jets and getting fired. The last order to Randall Lee Neville from CEO Conners was "no rolls."

It's also not a good idea. See for example the Lufthansa crash on 15 July 1964 where they tried to roll a B720 during a training flight:

http://aviation-safety.net/database/record.php?id=19640715-0

A jumbo barrel/aileron roll needs to be practiced in a highly-accurate simulator many times for performing on actual hardware to a high degree of repeatable success with least airframe wear, and then signed off by company folks and regulators. Otherwise, it's too risky.