If you do enough measurements on that new prompt then I don't see why this shouldn't be a paper. People overestimate the value of "grand developments", and underestimate the value of actually knowing - in this case actually knowing how well something works, even if it is as simple as a prompt.
Compare with drug trials: Adderall only differs from regular amphetamine in the relative concentration of enantiomers, and the entire value of the drug is in the measurements.
Compare with drug trials: Adderall only differs from regular amphetamine in the relative concentration of enantiomers, and the entire value of the drug is in the measurements.