If the bank offers a "credit card" access device as a new method of accessing the HELOC credit, I understand that we need a positive assent from the customer before providing the card.

Since the terms will be the same as the existing HELOC can we just provide the card in a mailing with the notation that all terms and conditions applicable to this account are currently in force with the existing HELOC agreement?

You need to review 226.9(b) - click to read a reg above and pick Reg Z.

Also remember to check state law, some prohibit the use of plastic to access a HELOC.