No, it's not realistically feasible to convert a 1969 Chevy Chevelle hardtop into a convertible. The structural differences between a hardtop and a convertible are immense. A convertible requires significant reinforcement in the chassis and body to compensate for the lack of a fixed roof. These reinforcements are integral to the car's design from the factory and are not easily added after the fact.
Attempting such a conversion would be incredibly expensive, time-consuming, and likely result in a structurally unsound and unsafe vehicle. The cost would far exceed the value of the car. You'd be better off buying a genuine 1969 Chevelle convertible.
