For Christmas club accounts, I assume they are considered time accounts so that you don't have to deal with statements etc. like you would for savings account. Once the check cuts for the account, we hold the account open for 90 days and if the cusotmer makes a deposit, the account is considered open again with no disclosures. If we changed the APY however from the previous term, would we need to dislcose this?

In my opinion, notification would depend upon what your initial Reg DD disclosure said at account opening. If you disclosed that the APY could change at any time and provided a number to call to get the current rate, you would not need to provide a notice. If you did not include this, I think you need to give prior notice of the change.