National bank is acquiring state bank that uses a FHLBB index on its ARM loans. The FHLBB index will be UNavaiable to the national bank after the acquisition because the acquired bank is in a different region from the national bank. Additionally, the index (from both regions) is not available to the public -- which is a requirement for an national bank when it makes ARM loans under an OCC regulation. Is national bank permitted to change the index even though the original index in the notes still exists (but is just not available to national bank)? If the national bank changes the index to the FHLBB in its region (as it is the most comparable index), would that be a violation of the OCC regulation that requires the national bank, when it makes ARM loans, to use an index that is available and verifiable by the consumer.

At my bank, our Promissory Notes have a clause allowing us to change the index. That may be a good starting point for you.