See link:  Hin-mediated Inversion on Positively Supercoiled DNA
Hin-recombinase requires negatively(-) supercoiled DNA for an efficient inversion. Results Section of Paper: Using plasmid pKH336, they introduced Chloroquine, a DNA-intercalating agent that unwinds the double helix upon binding. The paper goes on to say that Lk (sum of writhe or superhelical turns and twist); the unwinding effect of chloroquine-binding lowers the twist of the plasmid. The result is writhe increases because Lk does not change unless the backbone of DNA is broken and rejoined. Thus, a certain amount of chloroquine will remove supercoiling (relaxation) from (-)pKH336 and adds more supercoiling to (+)pKH336.
So it would seem we could in fact, alter the amount of negative (-)supercoiling.
Also, Dr. Eckdahl found that Novaviacin could also be used as well to the same effect.