Depends how you are arriving at that number.
If you are just choosing a number out of the air, problem.
If you have data relating to your loan portfolio that it has experienced a higher degree of delinquencies or losses on borrowers with scores of X or below, no problem. You will however at least every 18 months (I think it is) have to re-validate your data.
The opinions expressed are mine and they are not to be taken as legal advice.