With my first banjo I had Rick take my resonator and flange off so that I could experience playing something that had more of an open back sound. It was a great way for me to see what type of banjo I wanted to play. But a resonator banjo with the resonator and flange removed is definitely not the same as a true open back. They are very different because even with the resonator and flange removed there was still a wide metal tone ring. Where as in the open back the metal part of the tone ring is narrow; more wood less metal.
Makes a significant difference
From what I understand there are convertable banjos, but I do not know much about them.

Bonnie who hopes she got the banjo anatomy terms right