I am sure there are existing threads on this topic but my search skills are lacking.

For money market accounts that are converted to DDA due to Reg D limted transaction activity, is there a best practice for the YTD interest paid on the account, such as forfeiting it?

I'd be curious to know what my fellow bankers are doing; thanks.

I see no reason to pour salt into the wound. If the interest has already been paid, the fact that the account becomes a DDA on date X doesn't require any action on interest paid before date X, other than to report it under the IRS's 1099-INT rules (if they apply). If the interest has been earned and not paid, a best practice, IMO, would be to pay it.