50 C.F.R. § 29.43
If you already have a Service-issued permit, you may continue to operate according to the terms and conditions of that approval, subject to the provisions of this subpart. If you propose to conduct new operations, modify your existing operations, conduct well plugging or reclamation operations, or obtain an extension of the well plugging requirement to maintain your well in shut-in status, you must either amend your current authorization or obtain an operations permit in accordance with §§ 29.90 through 29.97 , Operations Permit: Application, and such new operations or modifications will be subject to the applicable provisions of this subpart. Additionally, your existing operations are subject to the following regulations:
50 C.F.R. §29.43