Answer:
No. Open-end loans are covered by different rules than closed-end loans. Workout provisions are covered by 1026.20(a)(4), but that entire section only applies to closed-end loans. HELOC changes are covered by 1026.9, and are very limited, even for rate reductions. The loan has matured, and as I like to say, it has turned into a pumpkin. No further modification can be made to it. The only options now are to do a brand new HELOC (subject to all Reg Z requirements); follow default provisions; or do a temporary forbearance agreement.
All this just to reduce the HELOC rate on a troubled line? Yep.