If you were to breed a Karma to a BEL your chances are 50% BEL (Lesser/Butter x Lesser/Butter) and 50% Butter Phantom.
I am sure you are well aware of two things:
1: A Karma ball python is a Lesser x Phantom Super BEL
2: Butter and Lesser are the same morph with two different names.
This means that the pairing of Butter BEL and Karma BEL would give 100% all white snakes with blue eyes but you will not be able to tell which is is Butter x Butter and which is Karma. Karma would obviously be worth more since it is a double genetic snake but you cannot sell it as a Karma since you do not know the exact genetic make up. This is why a lot of people do not breed BEL to BEL of different genetics. A Lesser BEL to a Lesser BEL has been done countless times.