For current Certificates, you would have to be guided by the agreement you have with these customers until their CD matures, in my opinion. You can't change policy midstream.
For Certificates you open going forward, I believe you can make the decision to only add interest to the CD or direct deposit it to an account they specify (not offer the option of a paper check). You'd have to change your disclosure to say so, of course.
I am unaware of any regulation that says you must provide paper checks for interest. However, be aware that this may be a very unpopular change with your customers. I know a lot of our customers really want that check mailed to them every month/quarter.
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