The model language in Reg DD Appendix B-1 for variable rate accounts shows two ways to disclose how the rate is determined:

"The interest rate on your account is based on ( name of index) [plus/minus a margin of ___]"

or

"At our discretion, we may change the interest rate on your account."

What should the bank disclose if the rate is based on an index plus a margin, but the bank wants to have the ability to change that margin at any time at its discretion?

Thanks,