You cannot impose different terms from your Plan Disclosure in the HELOC agreement without first providing the consumer an opportunity to reject the new terms. If they do so you must refund any fess they have already paid. From 1026.40:
(2) Conditions for disclosed terms. (i) A statement of the time by which the consumer must submit an application to obtain specific terms disclosed and an identification of any disclosed term that is subject to change prior to opening the plan.
(ii) A statement that, if a disclosed term changes (other than a change due to fluctuations in the index in a variable-rate plan) prior to opening the plan and the consumer therefore elects not to open the plan, the consumer may receive a refund of all fees paid in connection with the application.
Different floors constitute different plans/terms. If your disclosures show a 3% floor and your agreements show a 4.5% floor you do have issues.
You should, IMO, adjust the rates to match your plan disclosures and reimburse any overcharged due to the bank's error.
The opinions expressed are mine and they are not to be taken as legal advice.